where did the americans try to stop the British Army that was coming to attack Washington DC?

At the village of Bladensburg,about 5 miles northeast of Washington,24 August 1814.

However,it wasn't much of an effort.Despite heavily outnumbering the British (who only committed their advance guard to the battle),the vast majority of the American force soon ran off,despite the British having no cavalry or artillery.

Not where the Brits, actually mostly Canadian Militia were. Which is why the sack of Washington happened.

Canadian military personal get to wear a special 1812 pin on our uniforms commemorating the Canadian victory over the USA. I happen to be wearing mine, at the moment! :)

Your answer can be found here:

http://en.wikipedia.org/wiki/Battle_of_Bladensburg