Senate and House Republican leaders bluntly warned President Reagan yesterday that unless he compromises soon on deficit reductions, Congress will start writing a bipartisan budget of its own.

While stopping short of threatening an open split with Reagan, Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) and House Minority Leader Robert H. Michel (R-Ill.) told reporters that Reagan must make some move before the Easter congressional recess early next month. "I can't wait forever . . . . Time is sort of running out," said Baker, adding that he may ask Senate committees to begin work on a fiscal 1983 budget by the end of next week.

"They've got to make up their mind before we break here for Easter," said Michel. While he said he would not characterize this as a threat to break with the White House, he said Congress cannot delay a budget forever. "Maybe I got to move out on the shoulder and get around that doggone stalled caravan," said Michel.

Republican congressional leaders have been signaling Reagan in every possible way for weeks that his high-deficit budget is unacceptable to Congress. But, despite mounting frustration at Reagan's refusal to budge on such big-ticket items as taxes, defense and benefit entitlement programs, they had shied away from working with congressional Democrats on their own to draft an alternative budget.

Yesterday's statements--which one Republican aide characterized as a shot-across-the-bow warning to the White House that congressional patience is wearing perilously thin--came as White House chief of staff James A. Baker III began preliminary talks with the Democratic chairmen of the House budget and tax-writing committees about possible areas of compromise.

But it was not clear where the talks would lead, and White House communications director David R. Gergen said chief of staff Baker had authority from Reagan only to listen to the Democrats.

"He does not have authority to negotiate or proffer any deal," Gergen said. The possibility of a broader approach to compromise emerged yesterday as House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) made public a proposal he made earlier to Michel for a high-level bargaining group of nine members, including three each from the White House, House Democrats and House Republicans.

At least one of the three from the White House would have to be a top-level aide with authority to speak for the president, O'Neill said.

Later in the day Michel embraced the proposal, at least in general terms, and characterized O'Neill's approach as "conciliatory," even as to such details as bargaining over benefit entitlement programs, which are a particularly sensitive part of the budget for Democrats.

Michel indicated there was less flexibility on the part of the White House, although he insisted that he is "very optimistic" about an eventual compromise among all parties.

"Obviously there's got to be some movement from down the street the White House too," he said. Asked if it was true that there has been no such movement yet, he said, "That is probably accurate."

O'Neill was more explicit, saying there has been "no give whatsoever."

On taxes, Michel was especially insistent on more flexibility, saying, "there's just got to be some give down there" at the White House.

The Senate is scheduled to start its recess April 2, with the House following on April 7.

No House action on the budget has been scheduled until after the recess, which ends on April 19 for the House and April 13 for the Senate. The Senate Budget Committee, after several delays, is scheduled to begin writing a budget resolution next Tuesday.

It is not expected to finish by the start of the recess, however, and it is not clear whether a bipartisan consensus is possible without a signal of compromise from Reagan.

One major problem is that Democrats, fearful of being mousetrapped by Reagan in an election year, are reluctant to take politically risky positions on tax increases and spending cuts unless Reagan commits himself to them as well.

House Budget Committee Chairman James R. Jones (D-Okla.) underscored the point yesterday in discussing the limits of his talks with the White House.

"I don't intend to endorse anything that the president isn't involved in publicly," said Jones.

Jones said of any eventual compromise that Reagan, as well as O'Neill, "has to support it, endorse it, promote it." However, Michel expressed fear that positions would begin to harden if members went home without some kind of compromise in sight, making an eventual accommodation more difficult.