Wall Street suffered a rare courtroom loss on Wednesday after a federal judge sided with regulators who wanted to keep a closer eye on freewheeling derivatives trading.

In a 93-page ruling, the judge dismissed a lawsuit that financial industry groups filed against the Commodity Futures Trading Commission, a Wall Street regulator. The groups, the United States Chamber of Commerce and the Investment Company Institute, challenged a rule that forced mutual funds and other investment companies to register with the commission.

The industry groups contended that the rule was “arbitrary and capricious.” The trading commission, the lawsuit said, also failed to fully address the rule’s economic effects on the mutual fund industry.

But Judge Beryl Howell of the United States District Court for the District of Columbia rejected those claims.

“The C.F.T.C. not only provided justifications for the rule-making, but also explained the significance of the potential benefits of the rule-making,” she wrote.

The surprising victory for the agency and the Obama administration could have broader implications for the fight over a host of new financial rules being considered. Wall Street and corporate groups have won many other lawsuits challenging various financial rules, including several related to the Dodd-Frank Act.

“This is a total victory not just for the C.F.T.C., but also for financial reform,” said Dennis Kelleher, the head of Better Markets, an advocacy group that supports Dodd-Frank, which was created in response to the 2008 financial crisis.

The ruling, Mr. Kelleher argued, could cast a chill on other attempts to sue federal regulators. “Hopefully, the industry will see this as a sign to call off their war on regulation and the regulators.”

The mutual fund rule was not required under Dodd-Frank, but regulators say their effort was in the spirit of the law.

The legal battles have hinged not on the merits or constitutionality of Dodd-Frank but on whether regulators fully studied its effects. Wall Street has built its case around a legal provision that required regulators to evaluate the costs and the benefits any rule would impose on the economy.

The approach has worked. A federal appeals court last summer struck down the Securities and Exchange Commission’s proxy access rule, a Dodd-Frank policy that would have empowered shareholders to oust company directors.

Appeals courts have thrown out S.E.C. rules six times in seven years. In September, a federal judge vacated the Commodity Futures Trading Commission’s so-called position limits rule, which would curb speculative commodities trading.

In contrast, Judge Howell praised the trading commission’s work on the mutual fund rule. The policy, adopted in February, swept up mutual funds and investment firms into the agency’s new oversight of derivatives trading.

The firms are accustomed to only facing oversight from the S.E.C. The additional scrutiny from the C.F.T.C., the industry groups argued, was duplicative.

Judge Howell disagreed. In a sharply worded ruling that criticized the Chamber of Commerce and the Investment Company Institute for their “myopic view” of the rule, she took aim at the groups for their argument that the rule was unnecessary.

Saying the groups got “carried away by their own rhetoric,” she noted that the 2008 crisis was “due in significant part to derivatives trading, lack of transparency, and the lack of regulatory oversight, all of which prompted enactment of Dodd-Frank.”

It is unclear whether the groups will appeal. The investment institute issued a statement late Wednesday saying it was “disappointed with the court’s ruling” and was “reviewing the decision now and evaluating our options.”

The trading commission’s chairman, however, praised the ruling. “I commend the rule-writing, economic and legal teams at the C.F.T.C. for their excellent work and dedication,” said the commission chairman, Gary Gensler.

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