In a blow to millions of consumers who were awaiting the launch of a national Do Not Call list to restrict their mid-dinner calls from telemarketers, a federal judge in Oklahoma ruled Wednesday that the Federal Trade Commission lacks the legal authority to begin the system as planned next Wednesday.

The trade commission responded immediately, filing a motion of its intent to appeal the decision by U.S. District Judge Lee R. West. The agency also asked the court to allow it to implement the program with out delay pending a decision.

Representatives of Congress who supported the Do Not Call registry immediately began planning amendments to counter the ruling and grant the FTC authority.

"This decision is clearly incorrect," FTC chairman Timothy J. Muris said in a statement. "We will seek every recourse to give American consumers a choice to stop unwanted telemarketing calls."

But the ruling was cheered by representatives for the telemarketing industry, which has filed several lawsuits contending that the Do Not Call registry infringes on their First Amendment rights. The industry estimates that the provision would halve their business, costing $50 billion in annual sales.

Legal experts and lawmakers were surprised at the ruling, which at least temporarily halted a provision that was supported by President Bush and, apparently, a wide swath of the American public. About 50 million people have signed up to place their name on a list to forbid telemarketers from calling their homes. About three-quarters of the states have begun or plan their own Do Not Call lists, which would fold into the national registry.

Some predicted the decision would be a temporary setback.

If the courts move fast enough, legal experts said, the Do Not Call mechanism could still be implemented next Wednesday, as planned. Some noted the recent successful appeal that placed the California recall election back on track for Oct. 7, eight days after a ruling struck it down.

"It doesn't doom it," said Christopher Wolf, a partner with the Proskauer, Rose law firm in Washington. "It's a substantial roadblock. This just makes it a difficult last week before the list were to be implemented."

The plan had bipartisan support in Congress, and lawmakers voiced disappointment with the decision on an issue that has resonated with voters. House Energy and Commerce Committee Chairman Billy Tauzin, a Louisiana Republican, and Rep. John D. Dingell, a Michigan Democrat, issued a joint statement saying they believed the decision would be overruled.

"Contrary to the court's decision, we firmly believe Congress gave the FTC authority to implement the national Do Not Call list. We will continue to monitor the situation and will take whatever legislative action is necessary to ensure consumers can stop intrusive calls from unwanted telemarketers," they said.

The Direct Marketing Association filed the lawsuit in Oklahoma along with four other telemarketing companies. In a statement, the DMA said it sympathized with the millions of callers who want to stop telephone solicitations, but said it preferred to "self police" the industry.

"The DMA and its fellow plaintiffs are grateful that the Federal District Court in Oklahoma City understood and upheld the industry's belief that the Federal Trade Commission does not have authority to im plement and enforce a national do-not-call list," the statement said.

"We're excited about it," said Tim Searcy, executive director of the American Teleservices Association. "We know it's not the end of the road, but it's a good step."

The FTC predicts that a Do Not Call list would block about 80 percent of telemarketer calls. Charities, surveys and political pollsters would be exempt.

Telemarketers, however, have argued that the federal government cannot and should not pick and choose which interests have the right to communicate to the public.

"It says it's illegal for commercial speech, but OK for political speech," Searcy said. "They've created two classes of speech."

A business may also call someone on a "No Call" list if the person has bought, leased or rented its product in the past 18 months. Telemarketers can call if the person has called or in quired about something from the company in the past three months.

Phone sales companies would be required by the law to access the registry every three months and delete the phone numbers on it from their computer banks. The maximum penalty is a $11,000 fine per call if they call a number on the list. Whether -- or when -- they ultimately face that restriction is uncertain.

"If I had to predict, if we assume that this ruling stands in court, I would predict that Congress re-enacts the law," said Karl Mann, chairman of the marketing and e-business de partment at Towson University. "It's too popular. I think it's going to happen. It's just a matter of time."