With a Brazilian trio playing in the background and a packed nightclub in the middle of the afternoon, WWRC-AM (980) and about 150 friends saluted Felix Grant the other day on his 40th anniversary in Washington radio.

Grant, generally acknowledged as a premier jazz authority and the man who introduced many local listeners to the sounds of Brazil, Jamaica and many young musicians, stood on the stage at Blues Alley and received a wallful of plaques. One letter began, "Dear Felix," and continued, "Forgive the familiarity but since we both belong to the brotherhood of broadcasters, I didn't think you'd mind," and was signed by President Reagan. David Simon of the mayor's office read a citation that declared Nov. 19 Grant's day and praised his "distinctive, melliferous" voice. A message from Gov. Charles Robb declared the day Grant's in Virginia as well, and Maryland Gov. Harry Hughes also sent a message.

Since he joined WWDC-AM (1260) in 1945, Grant has become a legend, and periodically a cause, in Washington. He worked at WMAL-AM (630) for a total of 30 years, and when the station tried to move him from his weekday slot to weekends in 1979, it provoked a huge public outcry. In 1984 WMAL fired Grant, and shortly thereafter he joined WWRC, where he has been doing a Saturday show from 4 to 8 p.m. He also does a syndicated show for Studio Line Cable Stereo, a cable radio distributor.

"As someone who has spent a career watching the clock, I don't know where 40 years have gone," said Grant. Standing nearby was Stan Getz, who said Grant had never "sold out to schlock and rock." Later Getz serenaded Grant with a Brazilian melody. For the occasion, both men had a $25,000 scholarship named in their honor by the Blues Alley Music Foundation Inc. South Africa Special

WPFW-FM (89.3) will present a 17-hour discussion on the politics and people of South Africa Thursday, the first anniversary of the Free South Africa Movement. Last Thanksgiving Day, the Washington-based group started the daily protesting at the South African Embassy that inspired demonstrations across the country against apartheid. The show, 6:30 a.m. to 11:30 p.m., will include interviews with Del. Walter Fauntroy (D-D.C.), Rep. Mickey Leland (D-Tex.), Prince Boevi Zankli of Togo and representatives from the Washington Office on Africa, the African National Congress and the Free South Africa group. Producers Greg Anderson, Jimmy Gray and Mamzira Drupemba have put together what Anderson described as a "first national event." Anderson said they had invited a representative from the South African Embassy but hadn't received a response. Seasonal Drives

The ninth annual Project Harvest, a major undertaking of WHUR-FM (96.3), will culminate in a broadcast from the Old Post Office Pavilion Tuesday from 6 a.m. to 6 p.m. Until 1 p.m. the remote will be continuous; afterward, the staff will do periodic reports. The drive raises money for families with less than plenty at Thanksgiving and last year netted $12,000 plus food donations that filled a 55-foot trailer donated by Safeway Stores . . . In an event for Temporaries Food for Christmas, Doug (Greaseman) Tracht of WWDC-FM (101.1) will do a remote Wednesday tied into a private screening of "Rocky IV." The event, which is scheduled for Roth's Silver Spring West starting at 6 a.m., will include a boxing match . . . John Bodnar of WPKX-FM (105.9) will be the host for No Greater Love's annual senior citizen dinner Thanksgiving Day at Georgetown University. KIX listeners will serve as waiters and waitresses for the noon to 3 p.m. event . . . WMAL is one of five cosponsors of the Fuel Fund, the annual drive to help Washington area families pay their heat bills. The station is now running public service announcements in the hopes of surpassing last year's tally of $750,000 . . . WWDC-AM has a whole lineup of "Autumn Leaves" and "Count Your Blessings" scheduled for Thanksgiving Day from 6 a.m. to midnight. Fan Fever

Frank Harden and Jackson Weaver of WMAL, along with Redskin Mark Moseley, are inviting the public to sign a get-well banner for Joe Theismann Tuesday at noon at the Potomac Mills mall. All signers are being asked to donate 50 cents to Children's Hospital . . . WMAL will be airing all the University of Maryland Terrapins' basketball games starting tommorrow against Northeastern at 7:50 p.m. . . . Vince Bruce, who is known as Vinnie Brewster on WWDC-FM, has been selected "fan of the month" by the Washington Senators Fan Club. His name will be put in the hopper for "fan of the year," and his competition from the radio world includes Ernie Kayger, who is Ernie Kaye on DC-101, and Ed Walker and John Lyon of WMAL . . . Curtis Jordan of the Redskins is now doing commentary for WMJR-FM (107.7) weekdays at 8:20 a.m. Youth Passports

Members of Pyramid Communications, the youth-run media service, are hitting the road again. Next month Anitra Rowe, 10, producer of "New Attitude," which airs on WPFW on Saturdays at 9:45 a.m., is going to the Netherlands with the National Volunteer Center. Mandonna Shahvari, 15, the cohost of "All the Way," heard on WKYS-FM (93.9) Sundays at 11:30 p.m., is going to China to report on another trip of the NVC.