WASHINGTON – A federal judge is ordering the Federal Election Commission to tighten rules that govern political communications on the Internet and the ability of candidates to coordinate their activities with outside groups.

Judge Colleen Kollar-Kotelly of the federal district court for the District of Columbia ruled that the commission had passed rules that in some cases were “arbitrary and capricious” and “contrary” to the Bipartisan Campaign Reform Act of 2002, known as the McCain-Feingold law. She ordered the commission to rewrite 15 of the 19 regulations that two congressmen who want stricter rules had challenged in a lawsuit.

The ruling adds to mounting political pressure on the embattled enforcement agency to interpret and enforce the law more aggressively, although changes in the rules are not expected before the November elections.

New rules could have “far-reaching implications” for limiting political speech on the Internet, said the chairman of the commission, Bradley A. Smith. He said the commission has “ample grounds” to appeal the decision, which he described as “lackadaisical” in its reasoning.

The ruling comes as the regulator faces a series of similar federal lawsuits, including one filed last Friday by the reelection campaign of President Bush, seeking stricter regulation of independent political groups known as 527s.

The six commissioners, who often disagree over the content of rules, will vote on whether to appeal the ruling at a private meeting over the next few days, Mr. Smith said. In the meantime, the rules will be enforced as they were drafted before the judge’s ruling, he said.

Advocates of stricter campaign finance laws celebrated the ruling yesterday. They said it vindicated their claims that the commission is a “dysfunctional” agency that should be replaced.

The 157-page opinion is a “victory for democracy and clean elections – and a clear rebuke of the FEC’s repeated attempts to subvert campaign law and create new loopholes,” said Rep. Martin Meehan, a Democrat of Massachusetts, who brought the lawsuit in October 2002 with Rep. Christopher Shays, a Republican of Connecticut.

The opinion is also “further evidence that the FEC is a dysfunctional agency that does more to subvert the law than to enforce it,” Mr. Meehan said. The congressmen have introduced legislation to overhaul the commission. Similar legislation has been introduced by Senator McCain of Arizona and Senator Feingold of Wisconsin.

But Mr. Smith said the judge’s findings are “odd” because “none of the dire predictions about this law have come true.”

Advocates of stricter rules routinely say that the McCain-Feingold law has been effective at removing $500 million in previously unlimited contributions from the political system, he noted.

He said he thought the FEC’s regulations have been “very effective” in implementing the law.

But Judge Kollar-Kotelly said some of the commission’s rules on coordination run “completely afoul” of the law.

The commission’s rules on “coordination” of public communications between candidates and outside groups were too narrow and “would permit an evasion of campaign finance laws,” and “create the potential for gross abuse,” wrote the judge. The rules exempt coordination done more than 120 days prior to an election, and communications that do not specifically mention a candidate.

Judge Kollar-Kotelly also rejected a rule that excluded Internet communications from the rules.

Mr. Smith said he was concerned that the ruling appeared to cover a potentially broad range of political expression on the Internet, including unpaid political advertising.

“I think that’s called blogging to a large extent. Bloggers pay for a Web site. I think this has very far reaching implications there,” he said.

The decision “indicates that courts are going to say you can regulate to your heart’s content,” Mr. Smith said.

The judge also found that the commission’s definition of prohibited “solicitation” was too narrow because it prohibited candidates from “asking” for contributions but allowed “more nuanced forms of solicitation.”

The president of Democracy 21, a group that filed a friend of the court brief in the case, Fred Wertheimer, called the ruling a “massive and stinging repudiation” of the commission’s rule-making.

The campaign finance lobbyist for the advocacy group Public Citizen, Craig Holman, said the ruling would “put the FEC on notice that the courts will step in if it is deemed necessary.”

The judge issued the ruling Saturday, but it went widely unnoticed until yesterday.

Also yesterday, advocates of stricter campaign finance laws opened a new front in the campaign finance battle against what they called the last remaining “loophole” in the campaign finance law: nonprofit social welfare, labor, and business groups that participate in campaign-related activities.

While public attention has been focused on so-called 527 groups that have as their primary goal influencing elections, other nonprofit groups have been running political advertising with unregulated contributions from undisclosed donors.

Twenty-six such groups, known as 501(c)s after a section of the tax code, spent more than $91 million to influence at least 117 political contests in 2000 and 2002, according to a report released yesterday by Public Citizen. However, they reported only $12.2 million in electoral expenditures to the Istle majority of the groups backed Republican candidates, and at least 12 of them remain active, according to the report.

Some of these groups pose as “grassroots” organizations while being bankrolled by a few large corporate donors, the report states. Public Citizen launched a new Web site that monitors the groups’ activities, and asked the Internal Revenue Service to regulate the groups more closely.

Public Citizen asked the IRS to launch a formal investigation into the Pharmaceutical Research and Manufacturers of America for not disclosing some $41 million in contributions to four nonprofit groups that ran ads aimed at electing congressional candidates sympathetic to the Medicare drug law passed last year.

A spokesman for PhRMA, Jeffrey Trewhitt, declined to discuss the groups’ contributions, but said, “Any contributions we make are always within the letter and the spirit of the law.”