WASHINGTON — The Federal Election Commission can continue to regulate independent political groups on a case-by-case basis and does not need to adopt new rules to govern them, a federal judge said yesterday.

The decision was a blow to advocates of more restrictive campaign-finance laws, who say the lack of precise rules will result in widespread abuses of campaign spending in the 2008 presidential and congressional elections.

FEC lawyers argued that election commissioners were adequately policing the activities of so-called 527 groups, named after the section of the IRS code under which they are registered. These groups, which can raise money outside of federal limits, have become very influential in congressional and presidential elections.

The decision came one day after the FEC announced a settlement with a Democratic-leaning group that agreed to pay $775,000 for violating campaign-finance laws in 2004.

The civil penalty, announced Aug. 29, is the third largest fine ever levied by the FEC.

The group, America Coming Together, was an influential player in the 2004 election cycle, spending millions of dollars to mobilize voters in support of Democrats in key states.

The FEC found that ACT inappropriately used money raised outside federal election limits to help federal candidates. In a separate legal analysis, the FEC concluded that despite ACT's violations, the group did not coordinate its activities with the Democratic National Committee or the presidential campaign of Democratic nominee John Kerry. Such coordination is prohibited under federal law.

"The Court recognizes that the FEC has successfully brought enforcement actions against 527 groups (over the past year), which demonstrates that the case-by-case approach can be at least somewhat effective," U.S. District Judge Emmet Sullivan wrote.

Still, Sullivan said a rule governing 527 groups "appears to be quite reasonable." But he said he would defer to the FEC's argument that the complexity of the law requires flexibility that a rule would not provide.

The case stems from a suit filed by U.S. Rep. Christopher Shays, R-Conn., and former Rep. Martin Meehan, D-Mass. Both are the co-sponsors, along with Sens. John McCain, R-Ariz., and Russ Feingold, D-Wis., of a 2002 overhaul of campaign-finance law.

Campaign-money watchdog groups said the FEC's practice lacks clarity and results in enforcement actions that often come years after the infraction.

"The FEC cannot sit idly by and watch huge illegal expenditures made in the 2008 presidential elections, with the understanding that in 2011 the FEC may impose relatively small fines for these violations," said Fred Wertheimer, president of Democracy 21, an advocacy group.