The union that represents United Press International's workers said yesterday it will try to find a buyer for the 78-year-old news organization.

The union, which is deadlocked in negotiations with the wire service over possible contract concessions, said it plans to take a more active role in bringing United Press International out of bankruptcy. Talks between the union and the wire service broke off last month, and last week UPI said it would attempt to void the contract.

The Wire Service Guild said it had hired the high-powered investment banker Brian M. Freeman to be its financial adviser, assisting it in efforts to find a buyer. Freeman has worked for a wide range of labor unions representing workers at corporations engaged in takeover and bankruptcy battles. Most recently, Freeman successfully represented TWA's unions in their fight against Texas Air Corp.'s bid for the airline.

Freeman said he will talk with prospective buyers and "do a little bit of churning, letting people know we're here. . . . "

"Although it is late in the process" that began five months ago when UPI made its bankruptcy filing, "I think it is still timely," Freeman said in a press conference called by the Guild.

Freeman and Guild officials said they were optimistic they could find a buyer for the chain within two months.

UPI's own investment advisers, Bear, Stearns & Co. and Ladenburg Thalmann & Co., have set a Monday deadline for prospective buyers to submit written expressions of interest in the financially troubled company.

Until now, the bankruptcy court judge has barred the union from presenting its own reorganization plan or proposing a new buyer, leaving those proposals only to UPI's management and its creditors. However, the Guild -- which represents about half of UPI's 1,500 worldwide work force -- will try to convince the judge later this week to permit it to come up with its own solution to UPI's financial woes.

"No longer will this union, in representing the employes of UPI, engage in a passive and reactive role -- forced to choose the least damaging series of options in a scenario developed by corporate executives and outsiders," said Wire Service Guild President William Morrissey. Beginning today, the Wire Service Guild will be a major player in an effort to sell UPI as quickly as possible to the best available buyer. . . . UPI has one primary asset. It has no furnaces to repossess; no factories to mortgage. It has one asset -- its people."

Morrissey said that the union already has been in contact with several potential buyers and estimated that there were "five to 10" serious candidates. The union will "analyze and screen the range of potential purchasers of UPI to assure the emergence of the company from its bankruptcy proceedings," Morrissey said. He added that the Guild would consider all offers, including those that would give employes a share in the wire service's new ownership of the company. But, whatever the offer, he said, the union will "look most favorably on a party interested in preserving the largest number of jobs for the longest period of time."

Morrissey declined to say how much the Guild will pay Freeman for his services, saying it was an "internal matter." In previous cases, Freeman has commanded high prices, for instance, splitting a $2.5 million fee with investment bank Lazard Freres & Co. for his representation of TWA's unions.

Freeman said he has had no communication with UPI management. UPI officials said the company had no immediate comment on the union's action.