Western Union Corp. has decided to become a partner in a proposed nationwide satellite-beeper venture involving the financially troubled National Public Radio.

The New Jersey-based telecommunications company is taking what it described as "a major equity position" in National Satellite Paging Inc., a joint venture of NPR and Mobile Communications Corp. of America that hopes to offer a nationwide paging service through NPR's satellite distribution system.

Western Union declined to discuss details of the agreement or to say what impact it would have on NPR's finances.

However, a spokesman for MCCA, the nation's fourth largest paging company, said that "NPR's financial situation was obviously a factor" in Western Union's participation. Western Union and MCCA are partners in several other telecommunications ventures.

The spokesman also disclosed that serious discussions with Western Union began when the rocky state of NPR's finances was revealed several weeks ago.

National Satellite Paging, which was formed a year ago, is expected to file applications tomorrow with the Federal Communications Commission for a license to offer the nationwide paging service. Several other firms are also expected to compete for the limited number of paging channels.

Western Union's investment is expected to bolster the chances of the NPR venture winning the license. "Financial qualifications are one of the main things we look for in granting applications of any kind," said an FCC spokeswoman. The new venture would also allow Western Union to expand its efforts to diversify in the telecommunications field.

James T. Ragan, a Western Union vice president, said in a statement that, "although NPR has experienced fiscal problems, there has never been any question with regard to its technical and operational expertise in satellite transmission."