Washington — The President's dominant theme this fall will be that the Democrats are a bunch of ''budget busters'' who are attempting to obstruct the will of the American people.
Presidential strategists say they now have their ''big issue'': last week's defeat of the balanced budget amendment in the Democrat-controlled House of Representatives.
Using that vote as a campaign weapon, the President and Republican candidates will flail the Democrats, asserting that ''big spenders'' in the House defeated the amendment contrary to the clear desire of a majority of Americans.
Several days before the vote, the President's strategy became clear. One key administration figure confided that the White House wanted both the amendment and the issue - but that it would happily settle for the issue, if it came to that.
Actually, within the White House there was little expectation that the President would be able to win on the House vote. In fact, high-up administration officials were chortling when they were able to do what seemed the impossible: push the amendment out of committee and toward a House vote.
The administration applied all sorts of pressure and political guile to get the amendment up for a vote, but it eased off a bit when it came to the vote itself. That is, there was no full-court press with the President making calls to try to win.
Instead, the administration largely left it up to the congressmen to vote on their own - knowing, of course, that these congressmen would be feeling plenty of pressure from constituents who favor the amendment.
All of which has raised suspicion - at least among Democratic leaders - that the President and Republican politicians generally wanted the issue even more than they wanted the amendment.
''Look,'' one Democratic observer here says, ''if the amendment had been passed, it would have focused public attention on the huge federal deficit that has come about during Reagan's period as President. The administration really wouldn't have wanted that.''
But with the amendment losing, the President doesn't have to face the question: ''Why haven't you moved effectively to balance the budget?'' Instead, he's in a position to turn the question around and accuse the Democrats of failing to take the action necessary to bring about a balanced federal budget by 1986.
Thus, the President will, in his political forays around the country, seek to use his ''budget-buster'' theme to divert the attention of the voters from the recession, and, particularly, from increasing unemployment.
The question, say political observers here, is ''Will it work?'' Will the public buy the argument which says, essentially, that if the Democrats weren't restricting the President's efforts to cut spending, solutions to economic problems would be forthcoming.
Republican leaders have been saying for several weeks that this balanced-budget theme was an effective one - even before it was dramatized by the House vote.
But Democratic leaders say the theme will only play well among Republicans and conservatives.They contend that Democrats, and particularly unemployed Democrats, certainly won't accept this argument.
The Republican strategy rests on the assumption that there is indeed a conservative trend running in this country. Their hope: that the constitutional-amendment issue will inspire the same voters who elected Reagan to get out and vote Republican this fall.