NEW YORK — A federal appeals court yesterday said the government will be violating the First Amendment unless it takes steps to involve the courts when it demands secrecy from Internet service providers who give authorities private information on their customers.

The ruling by the 2nd U.S. Circuit Court of Appeals in Manhattan was a partial victory for the government.

A lower court judge had tossed out a provision of the USA Patriot Act that prevented ISPs and similar businesses from telling their customers if the government used so-called national security letters, or NSLs — investigative tools used by the FBI to compel businesses to turn over customer information — to demand private information about them.

The law lets the government acquire telephone, e-mail and financial records of Americans and foreigners without a judge’s approval.

But a three-judge panel of the appeals court ruled yesterday in Doe v. Mukasey that the law can be kept intact as long as the government agrees to initiate judicial review when the FBI seeks to stop NSL recipients from making disclosures to customers.

Melissa Goodman, a staff attorney with the National Security Project of the American Civil Liberties Union, said the ACLU was “obviously gratified that the court recognized there were serious constitutional flaws in the provision.”

She said the appeals court “recognized that the statute basically rendered the courts rubber stamps for the government’s gag provisions.”

Yusill Scribner, a spokeswoman for government lawyers in New York, said: “We are reviewing the decision and considering our options.”

The appeals court said the courts must be given a role in protecting rights even when the government says disclosure of information may endanger national security or interfere with diplomatic relations.

“To accept deference to that extraordinary degree would be to reduce strict scrutiny to no scrutiny, save only in the rarest of situations where bad faith could be shown,” the appeals panel wrote.

“The fiat of a governmental official, though senior in rank and doubtless honorable in the execution of official duties, cannot displace the judicial obligation to enforce constitutional requirements,” it added.

The ruling stemmed from a lawsuit filed in 2004 by civil liberties groups on behalf of an Internet service provider. The ACLU still is prohibited from disclosing its client’s identity even though the FBI abandoned its demand for records from the provider more than 18 months ago, the ACLU said in a release.