Rep. George M. O'Brien (R-Ill.), who spoke with top Syrian officials about seven Americans kidnaped over the last 1 1/2 years in Lebanon, said yesterday that the Syrians denied knowledge of the hostages' exact location and of those responsible for the abductions.

O'Brien told The Associated Press that the officials also pledged to work for release of the captives.

O'Brien, who returned to the United States Thursday, is the first member of Congress known to have spoken to Syrian President Hafez Assad about the hostages. He represents the district where one of the captives, the Rev. Lawrence Martin Jenco, grew up.

O'Brien said the Syrians disclaimed any knowledge of the hostages' health or living conditions, contradicting an earlier report from O'Brien's press secretary, Ted Cormaney, that Syrian officials "were very reassuring on the subject of health" and that the Syrian government was so well-informed that it knew the hostages had received medical attention.

Cormaney said today that the contradiction arose from his misunderstanding about what subjects had been discussed at the meetings.

The American hostages, kidnaped in separate incidents over a period of months, are believed held by Moslem extremists in Syrian-controlled eastern Lebanon.

The United States has hoped that Syria, whose influence was crucial to release of 39 American hostages from a hijacked jet in June, could facilitate release of these seven.

Meanwhile, in New York, the International League for Human Rights appealed to U.N. Secretary General Javier Perez de Cuellar to help free the seven Americans and six other men held hostage in Lebanon and said it has learned that the United States has not sought U.N. intervention in the matter.