WASHINGTON (AP) _ United Press International has received 25 offers from potential purchasers, ''including several substantial proposals from very well-heeled offerors,'' a federal bankruptcy judge said Monday.

Judge George Francis Bason Jr. did not identify any of the proposed investors. His comments came as he accepted a report prepared by UPI's investment advisers, Bear, Stearns & Co. and Ladenberg, Thalman & Co., and the Wire Service Guild's representative, Brian Freeman.

Bason said Jeff Peterson of Bear Stearns, Porter Bibb of Ladenberg Thalman and Freeman ''will be sifting through those proposals and consulting with offerors and with each other and reporting to their respective clients and to the creditors' committee.

''There is every reason to believe that this process will lead very soon to the filing of a plan of reorganization for UPI,'' said Bason, who called the timetable ''a truly remarkable achievement.''

Bason also said that UPI has operated in the black every month since it filed for reorganization under the bankruptcy law on April 28.

''Usually in a Chapter 11 case there is a period of losses for several months after the filing of the petition,'' he said. ''There has been no post- petition red ink in this case. That too is a truly remarkable achievement.''

In another report made in the nearly two-hour closed session and then read in open court, national mediator E.T. McMahon said representatives of UPI and its main union, the Wire Service Guild, will share information on any additional potential purchasers about whom they learn.

A working group composed of Luis Nogales and Raymond Wechsler, UPI chairman and president respectively, and Guild president William Morrissey and Freeman will jointly review various acquisition proposals as submitted to Bear Stearns and the Ladenberg firm.

''The objective of such review is to attempt to recommend the most desirable purchasers and-or investors to assure the continuance of UPI as a news-gathering agency,'' he said.

Bidders who have acknowledged an interest in buying UPI include Beurt R. SerVaas, chairman and controlling stockholder of the Curtis Publishing Co.; Joseph Russo, a Houston developer; and Max Hugel, a New Hampshire businessman.