NEW YORK, AUG. 20 -- Cardinal John O'Connor, archbishop of New York, presided over a meeting today between representatives of NBC and 2,800 striking union members that resulted in an agreement between the two sides to meet with a federal mediator.

The nearly two-hour meeting, called by the archdiocese of New York, brought together NBC President Robert Wright and AFL-CIO Secretary Thomas Donahue to discuss the dispute between the network and the National Association of Broadcast Employees and Technicians.

"At the conclusion of our amiable discussion, it was my understanding that both parties propose to resume discussion in Washington under the auspices of the Federal Mediation and Conciliation Service at the earliest possible time," O'Connor said in a prepared statement.

The meeting came just days before negotiators for NBC and striking union members are to meet in Manhattan at 10 a.m. Monday in their first discussions in a month. Officials from both sides intend at that time to discuss the impact on union members of NBC's recent sale of its NBC Radio Network to Westwood One Inc. of Culver, Calif.

Arthur Kent, president of NABET Local 11, said the meeting Monday may be expanded to include contract negotiations and may be moved to Washington. NBC spokesman Domenick Giofre said, however, that the network was trying to set the meeting with the federal mediator for Tuesday in Washington.

The talks will mark the first discussions between the sides since July 23.

At the western White House in Santa Barbara, Calif., meanwhile, technicians with CBS and ABC refused to cross a picket line set up by NBC NABET members around a hotel being used as a temporary White House press center by reporters covering President Reagan.

The refusal of ABC and CBS technicians and photographers to cross the picket line had little impact on the networks' ability to provide reports, since the network correspondents' stand-up reports are filmed at various sites around the hotel.

The NBC walkout has idled about 2,800 radio and television producers, writers, audio and video technicians, graphic artists and desk assistants in New York, Washington, Chicago, Cleveland, Los Angeles and San Francisco.

The union went on strike June 29 when the network imposed contract terms that NABET contends threaten job security