The chairman of the National Endowment for the Arts will continue to require recipients of federal arts grants to sign a controversial anti-obscenity certification, for the moment spurning a recommendation by his own advisory council that the pledge be dropped.

The decision to continue to require grantees to execute what critics have charged amounts to an anti-obscenity loyalty oath was conveyed to members of the advisory National Council on the Arts last Friday by NEA Chairman John E. Frohnmayer. A copy of Frohnmayer's two-paragraph letter was obtained by the Los Angeles Times yesterday afternoon.

In his letter, Frohnmayer said he had concluded that deleting the oath requirement -- as the council recommended, 17-2, earlier this month -- would be unwise in light of pending lawsuits against the NEA by two grantees who have rejected endowment money rather than execute the anti-obscenity certification.

Frohnmayer said he intended to put off any decision on adoption of the recommendation until a court ruling in one of the two grantee lawsuits is issued by a federal judge in New York. The case in which a ruling is imminent involves a constitutional challenge to the oath requirement by the New York-based New School for Social Research.

Also pending is a similar suit by choreographer Bella Lewitzky that is further from any court ruling. A number of groups and individual artists are expected to join in the Lewitzky litigation.

Floyd Abrams, a noted New York constitutional lawyer who represents the New School, branded Frohnmayer's decision as "nonsense," saying there is no legal obstacle to removing the oath. "Even if the court were to hold the oath constitutional, it would still be awful policy," he said.

The decision to leave the obscenity oath requirement in force during a time of the year in which the NEA typically makes hundreds of new arts grants came as a disappointment to one of the most influential members of the national council and appeared to have deepened dismay within the nation's arts community.

Wendy Luers, a council member who has been one of Frohnmayer's strongest supporters, said she had not seen the letter. Luers, however, said the decision raised concerns that large numbers of grantees would continue to be required to execute the oath while the court ruling is pending.

"A question, I think, is the deadlines for 1990 grants for people who have to sign the oath," Luers said. "What is this decision going to do to the recipients at this point who are protesting the language {or rejecting NEA money outright} between now and when a court decision is taken? I just don't know."