WASHINGTON -- President Bush speedily signed legislation yesterday to put a federal do-not-call list back on track, aligning the executive branch with Congress in seeking to protect Americans from telemarketers.

But the U.S. Supreme Court is likely to have the final word on whether Congress or states like Pennsylvania can pick and choose which telephone solicitations a citizen can choose to block.

The legislation pushed through Congress and signed by Bush yesterday responds to a ruling last week by U.S. District Judge Lee R. West in Oklahoma City that the Federal Trade Commission lacked the authority to enforce the federal "do not call" rules.

The new law makes that authority explicit.

Even before the president could sign the bill yesterday, another federal agency, the Federal Communications Commission, announced it would enforce the list if the FTC could not.

Telemarketers tried to prevent the FCC from doing so, but the 10th U.S. Circuit Court of Appeals in Denver deflected the attempt, an action that U.S. Supreme Court Justice Stephen Breyer later let stand.

All this maneuvering set the stage for the implementation tomorrow of the policy -- apparently by the FCC -- under which telemarketers can be fined for contacting consumers who have placed their names on the federal "do not call" registry. So far 50 million phone numbers have been registered.

But there remains a still larger legal shadow over the federal "do not call" program -- and similar arrangements adopted by various states. Shortly after Congress acted last Thursday to roll back the decision by the judge in Oklahoma, another federal judge in Denver invalidated the "do not call" program on constitutional grounds.

Because the federal "do not call" list made an exception for charitable solicitations, U.S. District Judge Edward W. Nottingham wrote, it treated telemarketers differently on the basis of the content of their speech, a violation of the First Amendment under U.S. Supreme Court precedents.

"Although the consumer does retain the choice [of] whether to sign up for the registry," Judge Nottingham wrote, "the government has removed the absoluteness of that autonomy by itself exempting certain types of speech from restrictions of the registry."

Nottingham concluded that Congress had a legitimate purpose in protecting consumers from disruptive or abusive telephone calls, but he rejected the notion that calls from profit-making enterprises are any more disruptive or fraudulent than those from solicitors for charities. Therefore, the program was not "narrowly tailored" to solving the problem, a requirement for laws that limit free expression.

Supporters of the "do not call" registry insist it is constitutional for Congress to pick and choose among telemarketers in creating a "do not call" list. A spokesman for Pennsylvania Sen. Arlen Specter, a longtime member of the Judiciary Committee and a co-sponsor of "do not call" legislation, said yesterday that nothing in Nottingham's decision had shaken Specter's view.

But at least one First Amendment scholar thinks Nottingham's ruling is "quite defensible." Eugene Volokh of UCLA Law School said the ruling was a plausible extension of past Supreme Court rulings, including a 1993 decision striking down the city of Cincinnati's policy of banning news racks containing "commercial handbills" while permitting newspaper racks.

Volokh said that if the 10th Circuit were to uphold Nottingham's constitutional reasoning, "the Supreme Court will have to consider the issue."

At stake in such a Supreme Court ruling would be not only the federal "do not call" registry but also similar programs by state governments that make a distinction between profit-making and non-profit telemarketers.

Pennsylvania's "do not call" law contains exemptions for charities as well as fraternal organizations, veterans groups and political fund-raisers.

Sean Connolly, a spokesman for Pennsylvania Attorney General Mike Fisher, said yesterday the attorney general's office was prepared to defend the constitutionality of the state law if it's challenged, but no challenged has been made so far.