THE SENSIBLE BILL to limit congressional campaign spending and take the tin cup out of Congress' hands is back on the Senate floor. The Democrats tried for three months last summer to bring it up, but weren't able to; the Republicans filibustered. It was all very decorously done; there were seven cloture votes, more even than on any of the great civil rights bills in the 1960s, but hardly anyone noticed, partly because the Senate did other business in between.

Now Majority Leader Robert Byrd is saying no more Mr. Nice Guy. He is threatening to keep the Senate in session around the clock and make the resisting Republicans filibuster in earnest, old style -- let them read the D.C. telephone book into the record on TV in an election year, all so the Senate can continue to float in a hot tub of campaign funds.

The Republicans have responded to this and other pressure by agreeing to talk. It's not clear how much that means. Minority Leader Bob Dole in particular has been in a difficult position on this issue. He is running for president, and doesn't want to appear to be quashing a white-hat bill. The talks, which began last week, let him and the party appear to be accommodative on the bill even if they are not.

In fact the Republicans can strike what would be a good deal for everyone and all the institutions involved, and they should try. The cost of office has become a curse and a disgrace. It now takes $3 million on average to win a seat in the U.S. Senate. To win a seriously contested seat or one in a larger state can cost four times that. The world's greatest deliberative body is a society of beggars.

The Democrats' bill seeks to limit spending, which has been soaring at a rate of some 20 percent per election cycle. The Supreme Court has said that unadorned limits would violate the free-speech clause of the Constitution. The Democrats have therefore made the limits voluntary. As in the presidential races now, a candidate would have to abide by the limits to be eligible for public funds, but could choose to forgo the limits and funds both.

Because the Republicans oppose public financing of campaigns, the Democrats have also backed the public money about as far out of the bill as they can. A candidate would be eligible for public financing only if he agreed to abide by the limit for his state, his opponent did not and his opponent then exceeded the limit. The public money would be an insurance policy. The bill would also limit the amount that any candidate could take from PACs in an election cycle.

The Republicans, better fund-raisers, say the bill would hurt their future chances, particularly in the traditionally Democratic South. The Democrats say they are willing to give ground here, too, by raising the initial limits in southern states. (The limits would be indexed thereafter.) They also say they might be willing to raise the present ceiling on individual contributions per candidate, lower the comparable ceilings for PACs and require public disclosure of contributions in the form of so-called "soft money" indirectly given. All these are important issues for the GOP.

The uneasy Republicans parry this by saying they are also opposed to spending limits and public financing on principle. That is less easy to satisfy. But the Democrats must ask them, and they must ask themselves, which do they think is worse: a small federal presence in congressional campaigns or a large For Sale sign on the Senate?