THERE ARE 27 senators running for reelection this year. Since their last election, they have raised $57.4 million in campaign funds, almost 30 percent of it from PACs, the giving arms of interest groups. Last year alone they raised $38.7 million, more than 2 1/2 times what they accumulated in 1981, the comparable year in their last election cycle. More than $12 million of that came from PACs, almost four times as much as PACs had given the same 27 six years before. The buying and selling of the Senate is out of control.

Just three senators -- Lloyd Bentsen of Texas, Pete Wilson of California and Howard Metzenbaum of Ohio -- raised almost 30 percent of last year's total. Mr. Bentsen, though no longer considered likely to face a particularly strong opponent, was the champ in this division of the Golden Gloves. The Finance Committee chairman raised $4.57 million, an average of about $88,000 a week, of which about $1.26 million ($28,000 a week) came from PACs. Mr. Wilson pulled in $3.44 million, only about a sixth from PACs. Mr. Metzenbaum chalked up $2.99 million, about $440,000 of it in PAC money.

When the Senate returns next week, a bill will await it to limit these amounts in the future. The legislation was on the floor for three months last summer. Majority Leader Robert Byrd, who is one of the 27 seeking reelection and who raised almost $1 million last year, more than two-thirds of it from willing PACs, tried seven times to win cloture. The closest he came was 55 of the 60 votes required. Two Democrats -- Howell Heflin and Richard Shelby of Alabama -- have joined the Republicans in blocking the bill. Only three Republicans -- Robert Stafford, John Chafee and Nancy Kassebaum -- have voted to allow the Senate to proceed, although they reserve the right to propose amendments.

The Supreme Court has said that spending limits and no more would violate the First Amendment. The Democrats have thus made the limits voluntary, part of a scheme under which some Senate campaigns could be supported in part by federal funds, much as presidential campaigns are now. A candidate who didn't want the funds wouldn't have to abide by the limits. In deference to the Republicans, who oppose public financing, the Democrats have also backed public money out of their bill until it is only an insurance policy. A candidate could get federal money only if he were abiding by the spending limit in his state and his opponent exceeded it. The spending limits, based mainly on population, would be indexed. There would also be limits on what House as well as Senate candidates could receive from PACs in an election cycle.

Republicans continue to oppose the bill, which they say would hurt them. Their case is weak. The goal of this bill is not to drive money out of its rightful and even healthy place in politics but to restore a lost sense of proportion before they hoist a bright white neon dollar sign permanently over the Capitol.