Was the American Constitution of 1787-1788 a conservative reaction to the democratic pressures of the Revolution?

To answer your question, possibly.  The Founding Fathers knew that the Articles of Confederation were inadequate. They only focused on the Congress, instead of an overall outlook on the new government, especially when it came to conflicts like Shay's Rebellion. The Founding Fathers realized that the new government needed more. They realized that to be free and independent from England, they needed a government to address all concerns of the people. 

The debate over the Constitution allowed a two party system to begin to form. In the case of revolutionary times, those two parties were defined by Jefferson and Hamilton. Jefferson wanted a strict interpretation of government and Hamilton wanted a loose interpretation to allow government to be flexible and add to it whatever was needed; and in Hamilton's views that was a national bank.   

So when it came to building a government, they first addressed a Congress. That is where you get two plans, the Virginia Plan and the New Jersey Plan. These were not necessarily conservative, but more along the lines of one state trying to trump the other. In the Virginia Plan, the authors wanted representation based on population (whcih makes sense because Virginia was the largest state at the time). The New Jersey Plan focused on equal representation. Here was the first of many compromises in the Constitution - they took both. The Virginia Plan was for the lower house or the House of Representatives and the New Jersey Plan was for the upper, more aristocratic house or the Senate. Then you have the compromise on slavery, the 3/5 Compromise. The biggest compromise was going to be a Bill of Rights that would be added to the Constitution. 

The goal was to get a government in place to begin to run the new nation and show the world that the United States was free and independent from England. The representatives knew that there were going to be things that they would need to address, like the Bill of Rights. The United States had to begin to act like a nation, build relationships and alliances with other nations, create an economic system to buy and sell goods, and begin to protect our new borders. Without a government, new chaos could set in and all that they had worked for might be lost and England could come back and try to regain control. 

The Founding Fathers understood that they would not think of everything and created an amendment process to allow the Constitution to adapt as we grow and change. That is why most historians refer to the Constitution as a living document. 

This question seems tricky due to the vocabulary.  In order to understand the question, we must first look at the principles behind the Articles of Confederation and the Constitution. Second, we'll talk about the modern concepts of Liberalism and Conservatism vs the 1700's definitions, and last I'll explain the answer to the question.  

Background: 

The Articles of Confederation were written immediately after the signing of the Declaration of Independence and during the preparations for the Revolutionary War. This new governmental document is filled with paranoia about the possibility of a new Parliament or King taking freedoms from the people of the United States.  I cite the 9th Article wherein Congress is the only entity that can declare war-- Unless the States are being attacked by "Indians"... or suspect that "Indians" might attack... or if their State is infested by Pirates... or (well it basically says that the state can declare war without Congress pretty much at any time.)  

The Articles of Confederation was a Confederate Government in that the states maintained the majority of the power. Votes in Congress had to be almost a unanimous decision in order to be enforced. Even then, State authority overrode most of the legislation. This led to the States being highly independent and above Federal law. Thus, in many states a Direct Democracy was theoretically possible, though it really didn't happen. Most states were run by the Governors and the State legislative structures.  

The Articles of Confederation's ensuing chaos led to financial issues and resulted in a political, military, and financial instability that threatened the United States after the Revolutionary War came to an end. It also led to the inability of Congress to control the States or protect from invasion. Inflation and England's conscription of ships led to increasing popular discord and the possibility of another country stepping in to control the floundering nation.  

The Virginia Plan, presented on the first day of the Constitutional Convention, was largely based on the writings of Charles Montesquieu and John Locke. Both enlightenment philosophers focused on the importance of democracy and popular sovereignty, and true to their writings, the original Virginia Plan was completely based on representation based on the population of the state. BUT, the Virginia Plan also built the new government as a central ruling authority by developing a Unitary Government system. This gave the Federal Government almost complete authority over the State governments. This was in complete opposition to the Articles of Confederation.  

The smaller states, which had an advantage in the political climate of the Articles of Confederation, balked at such a huge power grab by this new government. The Great Compromise brought elements of the Virginia Plan and the New Jersey Plan (Articles of Confederation) together by giving states equality in the Senate and Population based voting in the House. It also developed an unsteady "Balance of Power" between the States and the Federal Government. (Federalism)  State rights were further protected by the creation of the Bill of Rights- specifically the 9th and 10th Amendments which established State authority in things not specifically mentioned by the Constitution. This stabilized the balance of power.  

On to the Question: 

Where this question gets tricky is that it is using the word Conservatism. In general, modern interpretation of the word Conservatism is the antonym to Liberalism. Modern Liberalism tends to imply that Federal Authority over the states is necessary in order to enforce individual rights and move the United States in a positive direction. (i.e. The Supreme Court same sex marriage decision making GLBT marriages legal in every state despite the majority of some state populations being against it.) Therefore, Conservatism is the promotion of state's rights and popular sovereignty. This interpretation really CAN'T be used because it is modern, thus the question becomes confusing.

So let's look at it from a 1700's perspective:

During the time of the Revolutionary War, liberalism was the notion that citizens could rule themselves and a king wasn't necessary. The very idea that citizens would have a say in their government was a very liberal concept. The fact that the states maintained all of the rights didn't matter at this time, because democracy was in its infancy.  

Because of the citizens' call for Congress to establish some sort of stability in economics and law, (i.e. Daniel Shay) the Constitutional Convention did use a more conservative measure by applying a Federal oversight over the states with the Constitution. The call by the citizens for Congress to "do something" about several issues is the basis of democratic thinking. Creating a government that had authority over the people (in opposition to the Articles of Confederation where democracy ran willy-nilly) was like trying to reestablish a King or Parliament back into the United States. Federalist Alexander Hamilton actually suggested that measure.  

To recap- 

• Prior to the 1800's Conservatism would be returning to the more established lines of government seen in the world such as England's Constitutional Monarchy. In other words, returning a central authority that would control the states was a conservative measure.  

• This is in opposition to the Liberal ideals of Montesquieu and Locke, which freed citizens from a King or Parliament-like entity and allowed them to make their own laws. Under their ideals Popular Sovereignty would be the absolute.  (Every citizen in the United States voting on every law.)

• The phrase, democratic pressures is referring to the civic pressure placed on Congress prior to the Constitutional Convention to "fix" the mess created by the Articles of Confederation, the Revolutionary War, and issues with other nations. Because it is the general public placing pressure on Congress, it is an aspect of Popular Sovereignty, thus the foundation of true democracy.  

• Only once democracy was established in the United States as a stable government did notions of Conservatism and Liberalism change to their modern definitions.    

There is accuracy regarding the shift from liberal to conservative tendencies between the Revolution and the Constitution in American History.

One of the reasons is the difference between fighting for freedom and preserving it.  In the American Revolution, there was a frenzied approach to gaining freedom.  The Colonists were uncertain if they were going to achieve their end goal.  Certainly, the early setbacks of the American Revolution, the sheer imposing nature of the British, and the weight of doing something that had never been envisioned contributed to this feeling.  There was a liberalism to the American Revolution because the risks were so high and the rewards   so coveted.

In contrast, the American Constitution was more conservative.  Freedom had already been established.  The question that the framers of the Constitution had to address was how to preserve freedom and create a more effective government.  The framers were facing a nation in crisis. The autonomy intrinsic to the Articles of Confederation created a nation incapable of collecting taxes or enforcing laws.  Shays' Rebellion had also established a nation incapable of defending itself because of a lack of central authority. This need for power is  why the American Constitution could be seen as a more conservative reaction as opposed to the more democratic nature of the Constitution and its convention.