The union representing workers at United Press International announced yesterday it had reached agreement on terms of employment and other issues with two groups that have offered to buy the financially troubled news agency.

Separately, UPI Chairman Luis G. Nogales said the company will recommend its own selection of a purchaser on Monday. Thereafter, he said, UPI management expects to file a joint plan with its creditors and the union to reorganize the company and bring it out of bankruptcy proceedings.

The two announcements were made amidst indications that the list of possible suitors for the 78-year-old wire service, believed to number about a dozen as recently as two months ago, has been cut to three.

At a news conference yesterday, William Morrissey, president of the Wire Service Guild, identified the two potential buyers that have struck agreements with the union as Joe E. Russo, a Houston real estate developer, and Mario Vazquez Rana, a Mexican media mogul.

Morrissey said a third group is also actively interested in buying the company, though he declined to name the investor. He said, however, that he doubted anybody besides these three would be in the position to buy the company at this point, and that an announcement of a buyer acceptable to the union, creditors, and management could come as early as next week.

The guild, which represents about half of UPI's 1,500 workers worldwide, has recently stepped up its involvement in the efforts to solve UPI's financial woes, hiring Brian M. Freeman, an investment banker, as its financial adviser and actively screening the agency's suitors. The union has been hoping to capitalize on its role as a creditor, as well as its ability to influence UPI's significant labor costs, to play a major role in the negotiations about the company's future.

Although Morrissey refused to describe the specifics about the agreements with Russo and Rana, he said they were wide-ranging, not only dealing with terms of employment, but also with the method of paying off UPI's creditors. UPI reported debts totaling $40 million last April, when it filed for protection under Chapter 11 of the federal bankruptcy code.

Morrissey did say both agreements contain benefits for the workers, as well as the possibility of some concessions. He said both deals would be immediately discussed with the union's executive committee before the guild decided who to support as buyer. He also said the union would negotiate with the third party before making a recommendation.

In Houston, a spokesman for Russo also said that his understanding was that an investor group headed by the developer was one of the "final few" in the running for UPI. Spokesman Russell Rau refused to detail the nature of the negotiations Russo has carried on with the union, but he said that under Russo's proposal, UPI's workers would have an equity position in the company, as well as a say in management decisions.

Rau said that under Russo's proposal, the investor group would be prepared to pay creditors $14 million in cash at the time of the closing of the deal and was prepared to issue securities to pay off the rest of the claims. The investors also are willing to pledge an additional $26 million to ensure adequate working capital, as well as to satisfy the balance of creditors' claims, he said.

The spokesman said the investors planned to continue the company's basic wire service operation, as well as expanding into related areas in infomation technology