LOS ANGELES -- The Newport Harbor Art Museum has sued the National Endowment for the Arts, challenging a requirement that grant recipients pledge not to use funds for works that might be considered obscene.

The lawsuit, filed in U.S. District Court here, contends the NEA policy constitutes censorship and prior restraint. It seeks to prevent the NEA from withholding grants to artists who refuse to sign the pledge.

The NEA chairman, John E. Frohnmayer, also is named in the lawsuit.

The museum already has received NEA grants totaling $100,000 for four projects this year. Its board previously voted to refuse to certify compliance with the obscenity clause in a $20,000 grant to acquire works by living American artists.

"Having taken a position at the May board meeting not to comply with the NEA's restrictions, the museum is now taking the next logical step to test the NEA's position in the courts," said museum President Thomas H. Nielsen.

The museum is not attacking the NEA but the pledge requirement, said James V. Selna, an attorney representing the museum and one of its trustees.

"Our goal is to free the NEA from a restriction that hampers its ability to support the arts," he said.

The NEA requires grant applicants to certify that awards will not be used for works "which in the judgment of the National Endowment of the Arts ... may be considered obscene," according to the clause adopted by Congress last year.

Sen. Jesse Helms (R-N.C.) pressed for the policy after an outcry over NEA funding of such controversial projects as exhibitions of works by photographer Robert Mapplethorpe and artist Andres Serrano.

The policy is due to expire Sept. 30, but a Senate panel proposed a compromise extension Wednesday. Under the proposal, sent to the full Senate, NEA funding would be extended for five years and the government could move to recoup federal funds from any recipient convicted of violating obscenity or child pornography laws.