It has been a long time since two Republican congressional leaders faced a set of decisions as important to their party and the country as those now facing Senate Majority Leader Howard H. Baker Jr. of Tennessee and House Minority Leader Bob Michel of Illinois.

Baker's father-in-law, Sen. Everett McKinley Dirksen of Illinois, and Michel's predecessors, Charles A. Halleck of Indiana and Gerald R. Ford, had a similar role in the 1960s, when they controlled the fate of civil rights legislation. But they were opposition leaders, responding to the initiatives of Presidents Kennedy and Johnson. It was by rising above partisanship to embrace the cause of equal rights that they distinguished themselves and saved their party from what would have been a historic stain on its record.

Baker and Michel face what may, in some respects, be a more difficult role: to rescue a president of their own party from self-entrapment. You will not find either of these men admitting, for a moment, that is what they confront. But they know it, nonetheless. And so do others.

A top White House legislative strategist remarked the other day: "Last year, it was Ronald Reagan's year. This year, it's got to be a Reagan-Baker-Michel year."

What he meant was that in 1982, with a congressional election on tap, the limits of what the president accomplishes will be set by what the GOP leaders on Capitol Hill judge to be an acceptable political risk for their members. The Reagan aide was acknowledging that, for all his vaunted persuasive power, Reagan can order no kamikaze missions this year.

But his assumption, expressed on the day the Reagan budget was submitted to Congress, was that Baker and Michel would essentially determine how much of the second-year Reagan program becomes law. I do not think he contemplated that, within a week, the question might be turned around and become: how much of the Baker-Michel program will Reagan accept?

But that is what has happened. The Reagan budget flunked its first test of credibility in the financial markets, on Main Street and in Congress. The deficits--understated though they were--frightened all three of those sectors and deepened the doubts about the president's insistence on all of his military spending increases and all of his past and promised tax cuts.

While Reagan was out in the Midwest, describing his budget as "a line drawn in the dirt," Baker and Michel were hearing from a steady stream of their colleagues the nervous refrain that unreconstructed Reaganism might dig a deficit deep enough to bury all of them and their hopes for long-term Republican rule.

The response from the two GOP leaders was to encourage congressional Democrats to suggest various bipartisan initiatives to reduce the deficit, and to wigwag appeals to their friends in the administration not to shoot down exploratory offers.

The obstacles to a serious congressional initiative on the budget are formidable and the odds against its success are high. Reagan has put severe limits on Baker's and Michel's negotiating room by his adamant position on defense and taxes. In an election year, the Democrats will go only so far to help the GOP dig out of its own policy dilemmas.

But there is one action-forcing element in the situation which Michel and Baker both realize could enhance their leverage on the stubborn president. By April, the administration will need congressional approval of a debt-ceiling bill much higher than the $1 trillion limit (if you can call that a limit) now in effect, in order to accommodate the borrowing necessitated by the rising deficits. Without it, the government shuts down.

Long before Reagan lashed himself to the mast on his budget, Michel publicly warned him that it would be difficult to get many Republicans or Democrats to sign their names to such a resolution. Now, Senate Finance Chairman Bob Dole (R-Kan.) is talking about making the debt-ceiling bill a bipartisan vehicle that would send "the right signal" of a congressional determination to reduce the deficit--even at the cost of violating the tax and defense plans Reagan calls untouchable.

Neither Baker nor Michel is looking for a showdown with Reagan. But neither wants to preside over the liquidation of the most effective Republican congressional contingent this country has seen in years. Resolving that dilemma will test them as never before.