In reaching agreement with Senate Republican leaders on a proposed $778 billion federal budget compromise for fiscal year 1983, President Reagan has positioned himself for the showdown that must yet come if a final budget is to be put together. Mr. Reagan and party leaders can now argue that they have gone the distance in offering up a responsible budget. Still, a consensus between the White House and GOP-controlled Senate is only the first step in what is certain to be a difficult road in hammering out a final measure. For to get that final budget, there will have to be a compromise with the Democratic-controlled House. And it is far from certain that the Republican consensus reached this week will assure such an agreement.
Administration budget director David Stockman is on solid ground when he argues that the Senate compromise represents a ''good start'' on the budget process. That compromise came after outright rejection by the Senate Budget Committee of Mr. Reagan's original February budget proposal. In a sense, neither the administration nor the Senate leadership should feel self-satisfied for finally getting around to what they should have done weeks back, i.e., taking some positive action on the budget. But given all the private meetings and manueverings of the past few weeks, the public can welcome the fact that the budget debate is now taking place where it properly belongs - within the committee system of Congress and in the open glare of public exposure. This shift to a public forum is measured progress of sorts.
Given the substantial party-line vote on the compromise in committee, full Senate action looks possible. The House, meanwhile, is now moving ahead with its own version of the budget and will likely be prodded into speedier action by what is taking place in the Senate.
The potential for impasse, of course, remains great. The Senate Budget Committee measure represents some movement away from the original White House position in that it would raise $95 billion in new taxes over the next three years; cut $22 billion from defense spending during that period; and save $40 billion from unspecified ''reforms'' in the social security system. Democrats, however, will likely note that all this is not only less than Mr. Reagan offered in his bargaining session with Speaker O'Neill last week, but that ''unspecified'' new taxes and reforms of the magnitude of those now proposed are almost meaningless. The debate will come over the specifics. How, for example, will $95 billion in new taxes be raised?
Objections to the GOP budget compromise are not without foundation. Surely more than $22 billion can be cut from defense. And, as many economists note, it would be easier to defer or modify Mr. Reagan's third-year tax cut to bring in additional revenues than it would be to attempt to impose new taxes in an election year.
In short, the American people are still far from seeing any form of final action on the 1983 budget - so important to reassuring the financial community. But they can be modestly encouraged that the process of hammering out a compromise within the normal congressional committee structure is at long last underway.