Rep. John Murphy (D-N.Y.) has agreed to drop a $10 million libel suit against NBC in exchange for a prime-time retraction of a television report about his Abscam involvement.

The nine-term congressman, who faces two challengers for his Staten Island district seat, said yesterday the retraction scheduled for Saturday at 6:30 p.m. was the equivalent of a $4,000 free ad for his reelection.

Murphy sued the network for a Feb. 3, report that said he introduced immigration legislation on behalf of a phony Arab sheik seeking to buy political favors in the United States. The report, by correspondent Brian Ross, said the bill passed. In fact, no bill was introduced.

Murphy was indicted June 18 in the FBI's undercover Abscam investigation, during which agents posing as representatives of a rich Arab businessman offered bribes to congressmen in return for what prosecutors say were promises of political favors. He will go to trial Nov. 10 in Brooklyn federal court. Two colleagues, Rep. John Jenrett (D-S.C.) and former representative Michael O. Myers (D-Pa.), have been convicted in Abscam trials.

On Saturday night, NBC news will "regret" the error by saying "we have now learned that . . . statements by federal authorities" to correspondent Ross that Murphy introduced such legislation "were wrong," according to a letter to the congressman from NBC News."Congressman Murphy's subsequent indictment which alleges Abscam-related offenses does not claim that he introduced such legislation," NBC has promised to report.