ASHINGTON, Sept. 4 — Nearly everything about the campaign finance case that the Supreme Court will hear in a special session on Monday is outsized: four hours of argument (compared with the usual 60 minutes); eight lawyers (compared with the usual two); a lower court record of some 100,000 pages along with opinions totaling 1,638 pages that left the law in a greater state of confusion than it had been before.

Ten separate groups of plaintiffs are challenging 13 provisions of a 61-page statute that even specialists in election law describe as dauntingly complex, in what many regard as the most important election case in a generation.

In the 10 months the law has been in effect, the political system has scrambled to adjust to rules that the court may well change once again, just as the next campaign season gets fully under way. The most direct impact has been felt so far by the national political parties, with the Democrats suffering most from the loss of the big unregulated contributions known as soft money, and the Republicans getting most of the benefit from the doubling to $2,000 of the so-called hard money contributions to individual candidates.

Supporters argue that what is disturbingly outsized is not the Bipartisan Campaign Reform Act itself, but the flow of big money into politics that in recent federal campaigns has defied decades of attempted regulation and made the new law an urgent necessity.

The law's defenders describe it as a common-sense and constitutionally valid effort to fix demonstrated problems and plug the gaping holes in the Watergate-era law of which the new statute is technically an amendment. Its principal, although scarcely its only focus, is on soft money — the big corporate, union, and individual contributions to political parties that grew up outside the regulatory framework of the old law — and on corporate and union sponsorship of political advertising on television at the height of election season.

The powerful coalition of big business, organized labor, advocacy groups, political party organizations and Republican officeholders that sued to have the law declared unconstitutional depict it as a disturbing assault on the rights of free speech, political association and state sovereignty that is unjustified by anything in the voluminous record.

The opponents maintain that the law's sanctimonious approach to politics poses a greater threat to the health of the political system, particularly to the vitality of the parties, than do the concerns about corruption or the appearance of corruption invoked by its sponsors.

At the Supreme Court session on Monday, scheduled four weeks before the formal opening of the court's new term to accommodate Congress's request to accelerate judicial review of the new law, these arguments will be packaged not as policy but as propositions of constitutional law. But the boundary between law and policy, in this area as in others, is a porous one. The court's response may depend on which characterization most justices agree with: whether they see the law as making only modest and incremental revisions or profoundly startling changes.

Since its landmark ruling 27 years ago in Buckley v. Valeo, which struck down limits on campaign spending while upholding limits on contributions, the court has remained extremely attentive to campaign finance issues, creating a dense web of precedents. Based on the justices' previous votes, the court is appears closely divided.

Justices Anthony M. Kennedy, Antonin Scalia, and Clarence Thomas regard nearly all campaign finance regulations as infringements of free speech and will almost certainly reject the law's major provisions. In a dissenting opinion three years ago, Justice Thomas said contribution limits were "simply the suppression of political speech."

Justice John Paul Stevens is the most likely supporter of the new law. He has explicitly rejected the underlying First Amendment analysis in Buckley v. Valeo that equated money with speech. "Money is property; it is not speech," he wrote in a recent concurring opinion.

Justices David H. Souter, Stephen G. Breyer, and Ruth Bader Ginsburg are favorably disposed to campaign finance regulation, at least as a starting point. Justice Breyer said in a recent opinion that judges should defer to the "significantly greater institutional expertise" of legislators on the subject. The new law's supporters are urging deference to Congress as one of their main arguments.

That leaves Chief Justice William H. Rehnquist and Justice Sandra Day O'Connor. Their records make their votes unpredictable, with the overall outcome nearly impossible to forecast.

Another unknown is the timing of the decision. As their expedited schedule demonstrates, all the justices are aware of the political calendar. Their goal is almost certainly to have a decision by Dec. 15, when the court begins a four-week recess. That would give more time than the court took for Buckley v. Valeo, which was argued Nov. 10, 1975, and decided with a 138-page unsigned opinion 11 weeks later, on Jan. 30, 1976.

Congress acknowledged the new law's complexity, and the likelihood that different provisions might meet different fates, by permitting sections to be struck down individually without invalidating the entire statute. But because many of the provisions are conceptually connected, disentangling them may not be quite so simple and could have unintended consequences.

Two main provisions are at the heart of the current dispute. One bars national political parties and their committees from accepting unregulated "soft money" contributions. Parties may accept no more than the law's "hard-money" limit of $25,000 a year to any party committee. Related restrictions govern financial dealings between national and state parties and their candidates.

The second bans the use of money from corporate and union treasuries for "electioneering communications" — televised "issue ads" that, even if they do not use words to "express advocacy" like "vote for" or "defeat," seek to influence elections in the weeks before Election Day. These can be paid for only through a political action committee. Various disclosure and reporting requirements are also being challenged.

The last time the court held a special argument session during its summer recess was in July 1974 for the Watergate tapes case that led to President Richard M. Nixon's resignation.

As their guides through the law's maze, the justices will have a cast of legal stars, including the current and two former solicitors general. Solicitor General Theodore B. Olson and his principal deputy, Paul D. Clement, will argue in support of the law, along with Seth P. Waxman, solicitor general during the last four years of the Clinton administration, who represents Senators John McCain, Republican of Arizona, Russell D. Feingold, Democrat of Wisconsin, and the other chief Congressional sponsors.

Kenneth W. Starr, solicitor general during the first Bush presidency, and Floyd Abrams, a leading First Amendment lawyer, jointly represent Senator Mitch McConnell, Republican of Kentucky, who was the bill's leading opponent on the Senate floor and who, among dozens of other plaintiffs, won the race to have his name attached to the leading case, McConnell v. Federal Election Commission, No. 02-1674.

Three other lawyers will argue for coalitions of other plaintiffs. Briefs filed by the parties alone total more than 1,000 pages, not counting those filed by two dozen "friends of the court."

However brilliant the arguments, the justices and the cable audience might well conclude that the language of campaign finance requires simultaneous translation. While commonly known as McCain-Feingold, the Bipartisan Campaign Reform Act is almost invariably referred to by insiders as BCRA, pronounced BICK-rah. While the law's supporters refer to "soft money," opponents use the phrases "state-regulated" or "nonfederal money." What an ordinary person might call "campaigning," the statute refers to as "federal election activity."