The American Broadcasting Co. dropped court efforts yesterday to identify and punish whoever leaked the amount of its $500,000 settlement last month of a sex harassment lawsuit.

In return, the network received a statement of praise from the National Organization for Women's Legal Defense and Education Fund, which had been accused of violating an agreement to keep the settlement amount secret. The settlement was reached just before trial was scheduled to begin here in a case brought by Cecily Coleman, a former ABC employe in Washington, whom NOW was assisting.

However, late yesterday Linda Huber, one of Coleman's original attorneys, called the NOW statement a "sellout." She said, "Of course, ABC had the evidence of improper action by NOW-LDEF attorneys and extracted this statement as the price for aborting the inquiry."

In court statements last month, Huber and Mark Lane, who also represented Coleman, accused the NOW lawyers of divulging the amount ABC paid Coleman to get publicity for their organization. ABC attorney Stuart Gerson made a similar accusation.

The NOW-LDEF lawyers, legal director Marsha Levick and her associate Emily Spitzer, testified about the leak at a hearing held behind closed doors in early July by U.S. District Judge Barrington D. Parker. Before the courtroom was closed, a lawyer for the two had declined an offer by Parker to dispute the allegations.

Yesterday, the attorney, John Vanderstar, joined Gerson and Ralph Temple, Coleman's current lawyer, in asking Parker to keep that testimony secret along with what Coleman herself testified about the leak.

Last night, Parker had not acted on the secrecy request, which Huber strongly opposed.

In a joint statement after yesterday's hearing, NOW-LDEF said it "considers ABC to be a company of integrity and is optimistic about employment opportunities for women at ABC. NOW-LDEF looks forward to a productive relationship with ABC in the future."

ABC said it was "gratified" by the NOW-LDEF statement and "shares its optimism about their future relations."

Thomas Dyson, the attorney for James D. Abernathy, a former ABC vice president named in Coleman's suit, concurred in ABC's move to drop the sanctions motion.

In her $15 million lawsuit, Coleman, 30, alleged that Abernathy, 43, who was her boss, had made "unwelcome sexual advances" and that ABC fired her after she complained. Abernathy and ABC strongly denied the accusations and said after the settlement that they made "no admission of liability."

ABC said in court papers that Coleman had failed to complete assignments and was frustrated at not being hired on a permanent basis. Coleman was director of ABC's advisory committee on voter education before the 1984 election.

Yesterday, Huber said she had urged NOW to become involved with the case to help with fund-raising, but she said "they showed very little interest until it looked like a winner and would get publicity."

Officials of NOW-LDEF could not be reached for comment.