Rona Barrett, the irascible Hollywood reporter, signed with Mutual Broadcasting System this week to bring her unique entertainment reporting to a national radio network for the first time.

Scheduled to start April 15, Barrett will do three projects for Arlington-based Mutual: "Rona Barrett's Entertainment Report," a daily 90-second program; "Rona Barrett's Celebrity Talk," a daily 3 1/2-minute show; and breaking news reports on the network's other news and magazine shows. WTOP-AM (1500), WGMS-FM/AM (103.5/570) and WINX-AM (1600) carry Mutual's programs, but network spokesman Chris Durney said it was too early to say which stations have committed to carry the Barrett shows. The Near Future

Plans for "Washington: 2001," a year-long series on the future of the area, was announced this week by WMAL-AM (630). "For the 50th anniversary of the station we made a record album, pulling together some famous radio cuts. We said this time, that's fine, but that's history. We need to do something that looks at the future," explained Len Deibert, the station's news director. WMAL marks its 60th year on Oct. 12. The project examining the future Washington starts March 4 with a five-day look at the region's physical growth by Peabody-winner Larry Matthews. "What is this place going to look like? Fairfax County has 32 million square feet of office space. It plans an additional 40 million square feet. Tysons Corner will double. And Fair Oaks on Route 50 in the year 2000 will be bigger than Tysons," said Matthews. Other reports will survey families, health, housing, literature and inventions. WAVA of the Future

Charlie Brown and Irv Harrigan, known as Charlie and Harrigan, will join WAVA-FM (105.1) as the morning team within the next two weeks. The duo, which is making a transcontinental jump from KCBQ in San Diego, was described by WAVA's Smokey Rivers as "radio legends of the true sort." Said Rivers, "They have leanings toward good, solid political humor. They are brash realists and a lot of fun." Future Tennessee Williamses----

Two local students and a second-grade class from Elkridge, Md., are among the winners of the seventh annual Henny Penny playwriting contest, Children's Radio Theater, its sponsor, announced this week. Bernie Liu, 11, of McLean; Donna Mulvihill, 13, of Bethesda; 10 authors from Elkridge Elementary School, 7 and 8 years old; Winnie Phillips, 12, of Union, N.J.; and Eric Traynor, 14, of St. Petersburg, Fla., were the five finalists. Tom Dickson of Upper Marlboro won an honorable mention. The plays, which cover themes ranging from mud monsters to Cambodian refugees, will be produced at the Kennedy Center on April 13. The Washington-based CRT, whose Peabody Award-winning program is heard Saturday mornings at 10 on WPFW-FM (89.3), has just received a $35,000 grant from the Corporation for Public Broadcasting. Bluegrass Notes

For 40 hours, starting tomorrow morning at 8, bluegrass traditions will be the musical menu of WAMU-FM (88.5). This sixth annual festival will include Mike Kelley's trivia challenge at noon tomorrow and a repeat of the 1984 concert with The Lewis Family at 9 p.m. Sunday features a Top 40 countdown with Lee Michael Demsey at noon and a barn dance at 9 p.m. ? Grammy Grooves

WXTR-FM (104.1) will spotlight songs from 27 years of Grammy Award competitions from 5 tonight through 8 p.m. Sunday . . . WMAL will examine this year's Grammy Award nominees at 9:05 p.m. Sunday . . . WWRC-AM (980) gives in to Grammy fever on Tuesday, from 5 a.m. to 8 p.m. Other Grooves

WETA-FM (90.9) will offer a day of Handel tomorrow from 9 a.m. to 5 p.m. . . WHUR-FM (96.3) will broadcast a radiothon for the National Rainbow Coalition tomorrow from 4 to 7 p.m. The Rev. Jesse Jackson, president of the coalition, and entertainer Bill Cosby are the hosts. They will be joined for the first hour by journalist Jeremy Levin, the recently released hostage. Datebook

WWDC-AM (1260) is sponsoring a "Big Band" brunch Sunday at the Hyatt Capitol Hill, with the Frank Condon Orchestra from 10:30 a.m. to 2:30 p.m . . . WDJY-FM (100.3) is throwing a first anniversary party for itself this Sunday at The Third Edition, from 4 to 8 p.m. Proceeds from the $2 donations will go to the American Heart Association . . . WPFW is sponsoring "Ellington Revisited," a reunion of Duke Ellington band alumni, at Howard University's Cramton Auditorium Monday night at 8. Tickets are $15 . . . Hizzoner Marion Barry is scheduled to join Ernest White on "Crosstalk" Wednesday at noon on WDCU-FM (90.1) to discuss The State of the District . . . WPKX-FM/AM (105.9/730) takes to the roadside again on Thursday with morning mates John Bodnar and Paul Bottoms. The crew will be tied up at Bob's Big Boy restaurant on Route 236 in Annandale from 5 to 9 a.m. Black History Specials

At noon today WPFW features an installment of "Working Lives" that looks at mining camp life . . . On Sunday, WDCU spotlights "To Be Young, Gifted and Black," the prize-winning play by Lorraine Hansberry, with a cast that includes James Earl Jones and Claudia McNeil. Also at noon . . . WPFW will play the final segment of "Fanfare for the Warriors" at 2 p.m. Tuesday. This episode, produced by Renee Montagne and Thulani Davis, looks at musicians and the Vietnam experience.