ASHINGTON, Sept. 7 — For David Keating, executive director of a political advocacy group that promotes a free-market philosophy, the campaign finance law that will be the subject of an all-day Supreme Court argument on Monday has been a splendid development.

But for the Democratic Party, whose members provided the greatest support for the plan, it has proved more troublesome.

Although the Supreme Court has yet to decide on the constitutionality of the law, which took effect last November, some patterns have emerged in the practical effect the statute is having on politics.

One result is that groups that can solicit money to be donated directly to candidates, like Mr. Keating's Club for Growth, the Sierra Club and Emily's List, are poised to become more influential. At the same time, the national parties are having to adjust to the shift in the balance in fund-raising power to the single-interest groups.

In the last 10 months, the tension between everyday politics and the law has spawned a debate about whether the new restrictions really will change how campaigns are financed. Critics assert that little will be accomplished because money simply cannot be stopped from flowing into elections; supporters insist that the law already has had a profound effect by ending large unregulated donations to the parties.

At the very least, analysts on both sides agree, the law will give more power to groups like the Club for Growth, a Washington group that supports Republican candidates. When the club favors a candidate, it contacts thousands of the campaign's supporters, solicits donations and bundles them into chunks of money that are sent straight to the candidate.

"The law creates huge incentives out there for fund-raising that goes directly to candidates," Mr. Keating said. "That's exactly what we do."

While the prospect of greater influence delights Mr. Keating, it is deeply dismaying to Senator Arlen Specter of Pennsylvania, who was one of the few strong Republican supporters of the law. Senator Specter faces a primary challenge next year from Representative Patrick J. Toomey, who is being heavily subsidized by the Club for Growth.

At the heart of the system that Mr. Specter said he had hoped to eliminate with his vote was the distinction between limits on donations to a candidate and unlimited soft-money donations to the major parties. As long as the parties did not use the money to explicitly urge a vote for a candidate, they could and did spend it in ways to enhance their prospects.

Soft-money accounts grew by huge amounts in the last three presidential elections: the total raised by the six committees of the Democratic and Republican parties went from $86 million in 1992 to $262 million in 1996 to $495 million in 2000, with about three-fourths coming from businesses and executives.

But with the prohibition on large soft-money donations, there has been greater emphasis on soliciting contributions — under the new law, $2,000 per donor for each election — that go directly to candidates, the so-called hard money that groups like the Club for Growth specialize in.

"You have the same soft-money entry into the political field under a different banner," Mr. Specter said from his office in Philadelphia, where he was spending the evening phoning potential donors.

Senator Russell D. Feingold, the Wisconsin Democrat who was a co-sponsor of the legislation, said the law has wrought significant change.

"The fact is that about 10 months ago on Election Day, members of the Senate and House were still calling up corporations and labor unions and soliciting donations of hundreds of thousands of dollars," he said. "At midnight that became illegal and it has created a sea change in Washington."

Senator Feingold said that in the past, at the Tuesday caucus sessions of Republicans and Democrats in both chambers, the leaders would spend much of the time emphasizing the need for large donations.

Another early effect of the law is steeped in irony. The Democrats provided most of the support for the bill in Congress, while the Republican National Committee is challenging the law in court. But the Republican Party has been able to raise more than twice as much as the Democratic Party in hard money in recent months. In 1999, for example, each party had about $21 million on hand through June in a combination of soft and hard money. Through June this year, soliciting only hard money, the Republicans had $34.2 million, while the Democrats had $14.7 million

The reason, analysts say, is that the Republican Party has traditionally relied on a greater number of small donors while the Democrats have a smaller fund-raising base.

"Both parties are now investing heavily in improving their small-donor base, the people from whom they can get hard money," said Anthony Corrado, a professor of government at Colby College and an authority on campaign finance. "The Democrats have to play catch-up."

In another major development, there are efforts to set up groups to accept soft-money donations as the parties once did. Democrats have been quickest out of the gate, with one major group being Americans Coming Together, formed by labor, environmental and women's organizations with strong backing from George Soros, the international financier.

Ellen Malcolm is president of Emily's List, which tries to elect more women, and will be president of Americans Coming Together. She said she expects the new group to begin with a budget of $75 million, including $10 million from Mr. Soros.

The donations to the group are, like the now-outlawed soft-money contributions, unlimited and unregulated. While such groups may not coordinate their activities with the parties, there is little doubt as to their purpose.