This is also a matter of opinion.
There are, broadly speaking, two schools of thought on this. Idealists argue that America should try to spread its ideals. They argue that making more countries democratic will bring peace to the world. They point to the fact that, arguably, no two democratic nations have ever gone to war with one another.
Realists, on the other hand, say only force and the threat of force can bring peace to the world. To them, America's national security policy should only be driven by the desire to make the US stronger and more secure, regardless of whether that is done in an ethical way. They would point to the Iraq War as an example of how we messed up by trying to export our ideals instead of just concentrating on eliminating real dangers to the US.
As suggested earlier, this is a matter of opinion. Such a question has been brought out into the public discourse in the last nine years following the events of September 11. The argument which was posited to the American public at that time was that some level of restriction on personal freedoms, the basis of American ideals, was needed in order to preserve security and safety. While on some level, this had always been embraced (People always understood that, in public, all individuals had to endure some level of sacrifice of pure freedom in order to enjoy public safety and security), some argue that the measures passed in the days following September 11 went too far in removing much of American ideals in the name of a false sense of security. That is to say, just because ideals were suspended did not mean automatically that safety was guaranteed. Some argue that the passage of the Patriot Act, the detainment of "suspected enemy combatants" without trials or due process, or the notion of "enhanced interrogation techniques" did not serve to make the nation any safer.
Since this time, there has been a more collective voice that has asserted that American pursuit of ideals does not trade off with its pursuit of national security. This line of logic argues that American pursuit of national security aims can be consistent with its commitment to ideals. In this aim, both can be had, and not "either or."
The previous answer pegs the central dispute. Our ideals involve fairness, open and honest international communication, and the idea that consensus can be reached peacefully. On the other hand, war is unfair, and success in war is based on deception more than anything else. I believe Washington and the founding fathers were right in wanting America to lead the way into an era of open and plain-spoken diplomacy, and that alone could go a long way toward solving many of the world's problems. But let's not forget that most countries have always viewed diplomacy as war in disguise, and therefore full of deception. Clausewitz tells us war is politics by force, and let's realize that politics is economics primarily. It's not an accident that Western nations are led by the nose by corporate interests, nor that the "terrorist" element in the current world war crisis is led by rich people also. Ousama bin Laden was a financier, whose family is very wealthy, and he's not the only one. All governments, and non-governmental political movements, have always been led by economic motives. The rank and file may believe the ideals, but the leaders are in it for money and/or power.
America's ideals are important, otherwise we have nothing more to offer the world than the naked lust for power empires have always pursued. The most important point is for us not to forget the reason our country was founded, to give the world an example of a nation led by the people as an informed and empowered electorate. Unfortunately, the lack of real information in our news media and the complacency of the average citizen is a problem. The tendency is to let "the government" handle things, and what is the government but those we elect to do our corporate business? That business has become economic business, not the business of running the country for the benefit of the citizens per se.
But, and here is the real practical problem, intelligence gathering and war must be conducted by deceit or they will fail. In WW II Pres. Roosevelt spent years helping the British and Canadian intelligence services before the US was in the war. The entire Manhattan Project was a secret that began with the "Tube Alloys" project in Britain in the 1930s, and was built on weapons research which had gone on in secret since before the First World War. We must do that which is necessary, but at the same time not exceed what must be done. In the Second World War we had to let bombing raids kill thousands rather than let our enemy know we had broken their codes. Today, we may have to let unpleasant things happen rather than resort to torture or indiscriminate killings of people in the vicinity of legitimate targets, but that is the price we pay no less than the assassination of a real target, although that is murder, too.