A lawyer for the American Broadcasting Co. said yesterday he is considering asking a federal judge to overturn last week's agreement to pay nearly $500,000 to a former employe who filed a sexual harassment suit against the network, because the supposedly secret amount was divulged.

Attorney Stuart Gerson told U.S. District Judge Barrington D. Parker he was discussing the issue with ABC and James D. Abernathy, the former ABC vice president accused in the lawsuit of sexually harassing former subordinate Cecily Coleman.

Parker, conducting an unusual hearing at Gerson's request into who disclosed the amount of damages, suggested yesterday that "some additional testimony from the media" may be needed. Parker could impose legal sanctions, such as contempt-of-court citations or fines, against anyone who violated the settlement by disclosing its secret terms.

The Washington Post disclosed the damage total in its July 3 editions, the day after ABC agreed to make the payment to Coleman, who was once executive director of ABC's voter education program. No reporters have been subpoenaed.

Parker ordered his courtroom locked to the public for three days while he heard testimony from Coleman; her husband, James Prior, and two attorneys for the National Organization for Women's Legal Defense and Education Fund, Marsha Levick and Emily J. Spitzer, who aided Coleman. Yesterday, he listened in open court as lawyers in the case voiced their opinions on what should be done about the leak of the secret damage amount.

When Parker agreed last week to start the investigation, he said Coleman could negotiate the checks that ABC has given her as of noon today. Coleman asked that the deadline be kept.

Parker at one point said, "I don't see why these people, if nothing else happens between now and [today] at 12 o'clock . . . can't do whatever they wish to do with those checks." But Gerson asked that the deadline be extended on use of the money until he has questioned Kathy Bonk, a NOW spokeswoman, who will not return from a trip until July 22. Parker did not rule on whether Coleman can cash the ABC checks as of today, but he set a hearing for this morning.