Priding itself on an ability to break any story it goes after, the press is having difficulty penetrating one in its own back yard. When lords of the Fourth Estate refuse to answer questions, they refuse to answer questions. Government officials could take a lesson.

The story concerns the sale two weeks ago of United Press International, the nation's second-largest news service (the Associated Press is the largest). UPI was sold by its longtime owner, E. W. Scripps Co., to Media News Corp., which is owned by four newspaper and television executives from the South and Middle West. Before this group, National Public Radio negotiated as a potential buyer. What others have sought and failed to pin down is how much was paid for UPI and what the sources of money behind Media News are.

All Scripps president Edward W. Estlow would say in a telephone interview was, "We have not and will not disclose" terms of sale. "We're private and not obligated. . . . we're satisfied with Media News. Give them a chance." The new chairman of the board of UPI, Len Small, who is also vice president of a family-owned chain of daily and weekly newspapers, did not return my call. Elsewhere, Mr. Small has been reported saying that details of Media News' funding will not be revealed, but he will meet with UPI advisory board members to "satisfy" them about the new owners' plans for the agency.

Some board members are known to be troubled by the mystery surrounding Media News capital and ownership's plans for the service. The same goes for a number of UPI clients, including The Post. Executive Editor Ben Bradlee has written to Mr. Small to urge maximum disclosure.

Associated with Mr. Small are Douglas Ruhe, 38, and William Geissler, 36, who earlier had formed Focus Communications in Nashville. A fourth partner, Cordell Overgaard, is a lawyer and president of Community Cablevision. He has also been the attorney for the Small Newspaper Group.

Mr. Ruhe reportedly is to become chief operating officer of UPI. Mr. Geissler's role is unknown. Both are members of the Baha'i faith, which, without priesthood or ritual, is dedicated to ending racial and religious prejudice. Its center is in Wilmette, Ill., where the two worked for several years producing informational materials. Separately, Mr. Geissler is reported to have served a prison term from August 1969 to June 1970 for resisting combat duty in Vietnam. He has said he offered to accept a noncombatant role, but was refused by his draft board. Together with others, he was pardoned by President Ford in 1975.

This combination of circumstances has raised eyebrows and circumstances. UPI serves some 6,000 newspaper and broadcast clients worldwide and employs 2,000 personnel. At a time when rising costs are imposing tough decisions on editors, eliminating an agency's service--which can run to $50,000 a month--becomes a convenient one. Concerns about Media News' funding of UPI prompted a representative of Bankers Trust Co., which arranged the sale, to comment, "There is no Baha'i or other 'funny' money, there is no foreign money" involved. Earlier, Mr. Ruhe had told journalists, "We have enough money," and separately, "We have no intention of imposing our religious beliefs on UPI. We are dedicated to full and fair presentation of the facts and the truth in all matters. We will not interfere in the news coverage of UPI."

Still, concerns persist. UPI board member Richard Kennedy, publisher of the Waukegan (Ill.) News-Sun, put it matter-of-factly to Editor and Publisher magazine: "The public is the reader of the UPI service. If they don't look at the wire with full credence, then the service will suffer. If UPI is to be perceived as an independent news service and contributor of professional journalism in its purest form, then the partners should disclose their financial arrangements publicly."

UPI is 75 years old. It was begun by Edward WyllisScripps together with some other newspapermen, notably Roy W. Howard. It was Mr. Howard, saying "Write it for the Kansas City milkman," who set the agency's straightforward style. Alumni include Walter Cronkite, Harrison Salisbury, Howard K. Smith, Merriman Smith. Another, Robert Manning, former editor of The Atlantic Monthly, wrote recently how good it is to know that "old Avis will be here for another generation." The best assurance for that will come from less stonewalling by the new owners and more of the UPI style of telling it like it is.