It's a very broad question with no single answer, of course. But the dates of your question give us some meaningful context, in that in 1787, the Constitutional Convention began, and in 1857, the Supreme Court ruled in Dred Scott vs. Sandford that slaves were chattal property.
So we can generalize that the policy of the US government, as well as its intent, was to preserve the institution of slavery during these years, or at least not to pursue abolition, and they were quite successful at doing so. The Constitutional Convention purposefully avoided the question of slavery, for fear no unity between the states could be reached if a decision to abolish or keep slavery permanently was pursued. This is why the Constitution before the 13th amendment says virtually nothing about slavery. The other major motivation of the US government in this time period was to keep the country from splitting apart over slavery and its expansion, and they were somewhat effective in doing so by using political compromises that allowed the expansion of slavery west, but with limits.
The Supreme Court, throughout this entire period, upheld the property rights of slaveholders and refused to recognize slaves as human beings.
The Compromise of 1850 is where it started to unravel, in that popular sovereignty in the Kansas Territory was a disaster, and led to a bloody prelude to the Civil War.