Since Republican and Democratic leaders agree, it seems unanimous: There there ought to be a law reforming campaign finances to curb soaring costs and to create a fair, level playing field for House and Senate candidates.

The only trouble is that they cannot agree on what's fair and what's level.Neither side can afford to be against reform of a system almost everyone believes is too expensive, too distracting and too subject to abuses.

But the dominant Democrats aren't interested in legislating away the advantages of incumbents, and the minority Republicans want changes that could strengthen challengers.

So they argue about what is and isn't reform.

The most drastic of current proposals for campaign reform came from President Bush, in what was almost an aside as he called for a new ethics code for all federal office-holders.

"I believe we should eliminate contributions to candidates by political action committees, and I'll be consulting with the Congress about that, and I also oppose federal funding of congressional campaigns," Bush said.

Political action committees - PACs - are fund-raising groups organized among officers and other people associated with corporations, unions, interest groups and the like. The PACs raise money from their members and dole it out to candidates, mostly to incumbent senators and representatives.

PACs sprang up and multiplied, in number and in dollars, because of the stringent campaign contribution limits imposed in the reform wave that followed Watergate.

That's the trouble with reforms. As soon as they are devised, somebody invents a way around them, and sometimes the new reformed system is worse than the original problem.

Because there are more Democratic incumbents, nearly two-thirds of the PAC money went to Democrats.

Political action committees can give a candidate up to $5,000 for each election, primary or general.

Republicans do better at party fund-raising from individual donors. Neither party has a monopoly on fat cats, but the GOP has done a better job of cultivating the wealthy.

Those numbers point to the politics behind Bush's proposal for a flat ban on PAC contributions.

The president's proposal would limit the PACs right out of business, since they exist to make campaign contributions. Other Republican proposals would limit the size of PAC contributions as well as raise the limits on individual donations.

Either formula would work to the advantage of candidates challenging incumbents - which usually means Republicans in House elections, where the Democrats have an 86-seat margin. In the last elections, more than 98 percent of incumbent congressional candidates won new terms.

Democratic leaders want legislation that would set voluntary ceilings for congressional campaign spending, with a cap on PAC contributions as part of the formula. Their reform plan includes the public financing Bush rejects.

"He ran for president on public financing," said Senate Majority Leader George Mitchell, D-Maine. "If it's good for presidential campaigns, why is it so bad for Senate campaigns?"

Mitchell says the Republican goal is a setup that will preserve their advantage in raising money from well-heeled individual contributors.

They're right.