Senate Democrats rejected a Republican proposal to limit some forms of congressional campaign spending yesterday as the two parties, elbowing for political high ground on the issue, prepared for a showdown on finance reform as early as next week.

Meanwhile, House Democrats, after weeks of private negotiations, agreed to bring their own campaign finance package to the floor next week. The House will then have a choice of three reform proposals.

The House agreement enables lawmakers to vote on a proposal assembled by a leadership task force, a Republican alternative to eliminate all political action committee (PAC) contributions, and another Democratic alternative that includes tougher limits on PAC contributions and up to $100,000 in public financing for House races.

In the Senate, Republicans sent the Democrats a plan they called a "major move" toward compromise. It would restrict large out-of-state contributions but put no ceilings on aggregate spending from other gifts.

As outlined by Minority Leader Robert J. Dole (R-Kan.), it would ban PACs and impose state-by-state caps on a candidate's personal spending, out-of-state contributions exceeding $250 and money from PACs if the proposed ban on them is ruled unconstitutional.

They said that to reject this would show Democrats are not serious about overhauling Congress' widely criticized "money chase" for campaign contributions. Democrats had claimed Republicans want to prevent passage of strict spending curbs.

But within 90 minutes of the Republican presentation, Democrats denounced it as a rehash of earlier, rejected GOP proposals.

To create limits that exempt all home state money and out-of-state contributions of less than $250 is "a classic example of the exception swallowing the rule," said Majority Leader George J. Mitchell (D-Maine.). He said Democrats will insist on spending limits without such exceptions.

Sen. David L. Boren (D-Okla.), chief sponsor of the Democratic bill, said the Republican proposal could wind up "damaging the system more than it is now" by encouraging candidates to engage in single-issue politics to garner small contributions nationwide through direct-mail solicitations.

But Republicans contended that their proposal followed recommendations of a bipartisan panel appointed by Mitchell and Dole earlier this year, and said it would go far in driving "bad money," such as big out-of-state gifts, out of the system. A rejection now, said Sen. Bob Packwood, (R-Ore.) would show that Democrats "are not interested in a bill."

Democrats privately accuse Republicans of dawdling on the farm bill to squeeze campaign finance off the calendar as the Senate tries to recess for a month on Aug. 3.

While Democrats will not move immediately to force a campaign finance vote, Mitchell indicated they may eventually have to file for cloture to assure passage. "I think we know that point when we see it," he said. "I'm simply going to take this bill up and have action on it."

In the House, both Democratic plans would set voluntary spending limits of $550,000 per House campaign with inducements of lowered broadcasting and mail costs to candidates who agree to the limits. Both would lower individual contribution limits from $1,000 per election to $500.

However, the leadership task force proposal sets a 50 percent limit -- or $275,000 -- on PAC contributions to a House candidate and includes no public financing provisions. The other proposal, to be sponsored by Reps. Mike Synar (D-Okla.) and David Obey (D-Wis.), would set a 40 percent limit -- or $220,000 -- on PAC contributions and would permit only 10 percent of that total to come from large donor PACs.

Synar-Obey also calls for up to $100,000 in public financing of House races if candidates raise certain amounts in small individual in-state contributions. Their plan would also double the $100,000 public financing match to candidates whose opponents do not abide by the voluntary $550,000 spending limit.