David Ossman has been fired, effective immediately, as host and producer of National Public Radio's five-hour "Sunday Show."

"I was told to clean out my office at the end of the show on Sunday," Ossman said yesterday. "I have done that, and I have severed all relations with National Public Radio. All that remains is a financial settlement, which is now being worked out."

He had just completed his fifth month on the high-tech, wide-ranging show, which began beaming five hours of live programming on the arts to about 140 good-music stations nationwide on April 4, using NPR's satellite facilities. The show will continue to be aired on its previous schedule, using substantially the same staff and following the themes already announced for the immediate future -- a survey of Hispanic arts next Sunday.

Ossman reported that he will be replaced by two NPR veterans, Oscar Brand and Kaaren Hushagen, acting as co-hosts, with another familiar voice, Rod MacLeish, also becoming involved in the show "more as an editor." This report was, in effect, confirmed by John Bos, NPR's director of arts and performance programs, with the caveat that these replacements "have not been signed yet."

The identity of the replacements may serve as a clue to a long-range reorientation of the show, which will probably be toward concepts and approaches more traditional in good-music radio programming.

Brand was for years the host of NPR's "Voices in the Wind" program, which featured interviews with a variety of performing artists. He is the host and writer of a series of programs on Andres Segovia, which will be aired next season by NPR to mark the guitarist's 90th birthday.

Hushagen, who left NPR recently to become the assistant manager of the Baltimore Symphony, will continue in that position while returning to radio on Sunday afternoons. At NPR, she was associated with classical music programming, notably such series as "Quartessence," "The Art of Song" and "Cathedral, Court and Countryside," which dealt with specialized branches of classical music: the string quartet, art song and early music.

In contrast to the fairly tight focus on standard classical repertoire heard on most good-music stations around the country, the "Sunday Show" had ranged rather widely in its musical and non-musical interests, including quite a bit of material on visual arts, theater and dance as well as jazz and ethnic music, a survey of arts in the '30s and a series of regional surveys of the arts in various parts of the United States, such as the Mississippi Valley, New England and San Francisco. In its first five months, the number of stations using the show had remained fairly constant; last Sunday's show was carried by 143. But according to unofficial sources, some of the larger stations had dropped or were thinking of dropping the show. "We lost some and we gained some," was the only comment Bos would make on the program's audience size.

Last Sunday's program, after which Ossman was fired, was dedicated almost entirely to the work and influence of experimental composer John Cage, who was celebrating his 70th birthday. Cage's work is highly innovative but hardly calculated to please most enthusiasts of mainstream classical music.

"The show is not meeting the exhortations of the stations, and that's our business," said Bos. At the same time, he expressed admiration for some of the show's accomplishments. "They tried to make a seamless five-hour program," he said, "and they came close. They developed an audio texture that was gorgeous. David's approach was that the show, the five hours each Sunday, was to be an artwork in itself.

"I disagree with that; I don't think it corresponds to the way most people actually listen to radio. I think that radio -- the craft of radio -- can be a translation medium for other arts that exist independently. A medium for the arts: That's what we painted for the National Endowment and more than 800 arts organizations across the country -- a sort of audio funnel for a lot of that collective experience."

One of the show's problems was that Ossman, who was hired as executive producer, was unable to find a host who met his specifications and began to serve as host himself. This left the show without an executive producer distinct from the host. NPR has been searching for someone to fill that position for the last two months and is still searching. "I will be acting as executive producer until we find one," Bos said.

Ossman, 45, is a veteran radio performer, writer and producer -- probably best-known nationally, before the "Sunday Show" began, as a founding member of the "Firesign Theater." Still recovering from the surprise of his abrupt dismissal, he said that he and his wife, Tiny, are now "considering all our options."