Mario Vazquez-Rana, the Mexican publisher who rescued United Press International from bankruptcy two years ago, announced last night that he has turned the embattled wire service over to a media investment group run by current and former executives of Financial News Network.

In a statement issued by UPI, Vazquez-Rana said he had granted the media investment group, WNW Group Inc., an "irrevocable proxy to operate UPI for at least 10 years in exchance for present and future financial considerations totaling more than $55 million."

The statement did not call the transaction a sale, and officials of UPI and WNW could not be reached for comment. But Sean McCormally, chairman of the Wire Service Guild's negotiating committee, speculated that the arrangement might have been structured to get around a stipulation in an agreement between the Guild and Vazquez-Rana that stipulated the Guild was to be informed of any sale involving more than 10 percent of UPI, and an employee stock ownership plan would be given the right of first refusal.

Dr. Earl Brian, chairman of Financial News Network, is also chairman of WNW. Paul Steinle, 48, former president of FNN, will be the president of UPI and will have total operational control of day-to-day management.

The transaction is the third change in ownerswhip for UPI in six years, which reportedly has not had a profit since the 1960s. Vazquez-Rana was reportedly losing $1 million to $2 million a month, and for months was rumored to be searching for a buyer.

Vazquez-Rana paid $41 million in 1986 to acquire UPI in the course of a Chapter 11 bankruptcy proceeding. FNN was a rival bidder for UPI in 1986, and when it lost to Vazquez-Rana it charged the parties had unlawfully conspired to determine the outcome of the bidding.

Steinle said, "We have access to sophisticated communications technology which may be cost-effective for UPI, experienced management, capital resources and computerized editorial processing capability."

Vazquez-Rana said he "considers his task of investment in UPI completed at this time."

Directors of WNW are J. Alexander McMahon, chairman and professor of the Health Services Administration Department at Duke University; James Thistle, director of the School of Journalism, College of Communications, Boston University, and Erik Hendricks, executive director of the Pennsylvania Society for the Prevention of Cruelty to Animals.