Right on the heels of a successful fundraiser, WAMU-FM (88.5) abruptly fired five of its seven news staffers last Friday, citing the cost of running a full-fledged news department, the need to shift resources because of financial constraints on public radio, and the loss of audience during the local portions of "Morning Edition."

WAMU, a public station owned by American University, had one of the largest local radio news departments. It produced 18 minutes of local report for National Public Radio's weekday news program and had regularly won awards for its competitive reporting. Its cadre of a dozen regular arts and political contributors, considered an important source of information, was also terminated.

"We didn't do this because we can't afford a news department, but there are other things we need that we can't afford," said general manager Nina Kern. "With the constrained resources of any public radio station, we have to put our resources where they have the greatest yield. We freed up some funds that we will be reinvesting in some physical plant and other staffing needs."

The action will enable WAMU to redirect more than $100,000 of its $1.3 million budget to other projects, said Kern.

The station said its own audience research showed listeners were leaving during the local segments, a finding former staffers vigorously disputed.

Though the audience during the morning has increased over the last three years to 97,600, station management found that the increase followed the trimming of local news. "I looked at the raw diaries and found people leaving when we did the local news at the peak hours of 7:15 and 8:15 a.m. In the last survey, we had four people tuning in and 21 tuning off at 7:15 a.m. and five tuning in and nine tuning off at 8:15 a.m.," said program director Craig Oliver.

The action seemed oddly timed since the station had just raised $231,500 in its annual fall drive, during which it continually stressed its local news coverage. Kern said the decision to eliminate the positions had been made before the fundraiser. "The fundraiser wasn't an issue one way or another. One doesn't arrive at a decision like this and then act it out tomorrow," said Kern.

Some news and funding sources expressed displeasure with the decision, which leaves all-news WTOP-AM (1500), WMAL-AM (630) and WHUR-FM (96.3) as the principal stations with news-gathering staffs.

"It decreases the community's ability to receive a broad variety of news and information of interest to them," said Annette Samuels, press secretary to Mayor Marion Barry. Thea Marshall, president of a Washington-based public affairs production company that paid $800 for 20 underwriting spots last month, reacted angrily. "We are withdrawing our support because I believe they reneged on the contract to provide local news. I am offended by listening to the report of a volcano in Hawaii and the other filler instead of local news," said Marshall. Kern countered, "We are not in any way reducing local news. What we are reducing is the expensive highly produced features. We have not relinquished our responsibility to local news."

Fired were news director Anne Boozell, news editor Matt Coates and reporters Ken Barcus and Julie McCarthy. A fifth vacant position was eliminated.

"It is what happens in radio," said Boozell, an employe of WAMU for three years who went through a similar purge at the old WEEL. "As soon as the station gets in financial difficulty, they cut the news department. You know it's the finances because the budget gets tight, you can't get approval for any spending. Last year the university gave 7 percent raises and everyone at the station got 4 percent." Last year one segment of local news in the morning was also eliminated.

Right now Bill Redlin, local host for "Morning Edition," and newscaster Mark Boardman will do a 3 1/2-minute wrap-up of news, traffic and weather from 6 to 10 a.m. and the station will use its staff, NPR and Associated Press summaries during the day. Halloween Plans

WWDC-AM (1260) feels the need to get started on Halloween mania early with a dance tonight at 8:30 in the Sheraton Inn Northwest ballroom in Silver Spring . . . Tomorrow Adam Smasher of WWDC-FM (101.1) is having a party with the Vienna Jaycees for their various charities at the Vienna Community Center from 8 to 11 p.m. . . . On Halloween night Tom Kent of WAVA-FM (105.1) will broadcast live from the Sheraton Potomac Inn in Gaithersburg starting at 6. Crockett of WBMW-FM (106.7) will be broadcasting from Annie's in Georgetown from 7 p.m. to midnight. Chris Jagger of WRQX-FM (107.3) will be down the street at the Bayou from 7 p.m. to midnight. WKYS-FM (93.9) is sponsoring a "Thriller" party at Triples, 3714 Branch Ave. in Hillcrest Heights, starting at 7 p.m. Dexter Manley will judge the costumes and the Easter Seal Society will benefit. WLTT-FM (94.7) will sponsor a dance at Deja Vu at 2119 M St. NW starting at 8 p.m. WHUR-FM (96.3) is having a dance at the Old Post Office from 9 p.m. to benefit its Project Harvest food-a-thon for needy families. A Classical Tally

WGMS-FM/AM (103.5/570) raised $87,000 last weekend for the Washington Opera's new production of Donizetti's "The Daughter of the Regiment," which will be staged at the Kennedy Center Terrace Theater from Dec. 28 to Feb. 1. An Anniversary

Paul Anthony, host of "Jazz Unlimited," will present a special Big Band party tomorrow at his new time, 8 to 11 p.m., to celebrate his fifth anniversary with WGMS. Anthony is also doing a daily program of American music for the Voice of America's new channel geared to younger Europeans.