Senate leaders agreed yesterday to seek a compromise on congressional campaign-financing legislation in hopes of breaking a nearly yearlong deadlock and avoiding round-the-clock sessions that have been threatened by Majority Leader Robert C. Byrd (D-W.Va.) if the impasse persists.

As the Senate opened its election-year debate on the controversial measure, Sen. Alan K. Simpson (R-Wyo.), minority whip, suggested outlines for a compromise that drew a favorable response from Democratic leaders.

But negotiators appointed by the two parties reflected sharply opposing points of view, and senators continued to stake out positions that appeared to leave little ground for compromise on the most contentious points.

At issue is legislation sponsored by Sens. Byrd and David L. Boren (D-Okla.) to encourage candidates to abide by spending limits and to set aggregate limits for contributions from political action committees (PACs). Candidates who adhere to spending limits would be eligible for reduced postal and broadcast advertising rates and for public financing to offset spending by an opponent who exceeds the limits.

Republicans object to spending limits and public financing and have countered with legislation that would reduce limits on individual PAC contributions and tighten

rules for disclosure of campaign finances.

Although the Democratic bill has 52 cosponsors, action on it was held up last year by a Republican filibuster led by Minority Leader Robert J. Dole (R-Kan.), a leading candidate for the Republican presidential nomination. Democrats say that they are still five votes short of the 60 necessary to end debate and bring their bill to a vote.

Dole supports the attempt to reach a compromise. But it was not clear whether he backs Simpson's suggestion that Republicans would be willing to discuss spending limits if the Democrats would consider tightening rules governing phone banks and other services commonly provided by labor unions in backing Democratic candidates.

In suggesting the trade-off, Simpson said, "If they {the Democrats} will get serious with us on soft money, in-kind contributions, we will get serious with them on taxpayer financing and limiting PACs." Asked by Byrd whether that meant limits on campaign spending as well, Simpson said, "Overall campaign expenditures is not off the table. We will put everything on the table."

Democrats welcomed Simpson's proposal as a good starting point for negotiations, but at least two of the Republican negotiators, Sens. Mitch McConnell (Ky.) and Rudy Boschwitz (Minn.), expressed doubt that spending limits would be acceptable.

Negotiations are scheduled to begin today and continue as long as they appear productive, although probably not beyond the end of the week, Democratic strategists said. Before the start of yesterday's debate, Byrd warned that failure of the talks and resumption of the GOP filibuster would result in tough countermeasures by the Democrats.

"If there's a filibuster, it won't be a gentleman's filibuster," Byrd said. "We won't begin at 9 and end at 5." Aides said Byrd, Boren and other Democratic leaders have talked of all-night sessions to wear down opposition to the measure.

Moreover, one strategist said, Democratic senators are prepared to take the floor to challenge Dole on the issue, even if he is campaigning out of Washington.

"He won't just be able to hide behind a negotiating group," the aide said.