When radio stations worldwide simultaneously aired "We Are the World" last week, President Reagan was tuned into WTKS-FM (102.3) aboard Air Force One.

The White House Communications Agency called WTOP-AM (1500), a station the president often listens to in flight, and asked if it was going to play the song, according to station spokeswoman Susan O'Malley. All-news WTOP was not planning to air the all-star song for famine relief but arranged to patch its sister station, WTKS, to the jet. "After it was over, they called to say thanks," said O'Malley.

WGAY-FM (99.5) was another of the few stations that didn't play the song. "We had quite a few calls, about 25 to 35," asking why it didn't, says Bob Chandler, operations manager of the "beautiful music" station. "We explained that it didn't fit the format and we had supported similar efforts through public service. It was so much out of format that if I had played it, I would have gotten many more calls. "It's the Coast Calling

WTOP has signed up for "Rona Barrett's Entertainment Report," which debuts on Mutual Radio Network Monday. The 90-second report from one of the best-known entertainment reporters will be aired at 11:42 a.m. A Music Search

WWDC-FM (101.1) kicks off its second annual search for the best home tape from area musicians Monday. For a month the station will be collecting cassettes -- one song per tape -- from individuals and bands; the winner gets a recording session. The competition is stiff; last year the station received 200 entries. Live Theater

The winning works of the annual Henny Penny Playwriting Contest will be aired at 10 a.m. tomorrow from the Kennedy Center over WPFW-FM (89.3). Tempestt Bledsoe, an actress from "The Cosby Show," will be the host of the children's presentations. Schedule Shifts

Steve Ember takes on a new title, "Ember at Large," and a new time this weekend as he moves his show to 3 p.m. Sunday on WETA-FM (90.9). Starting Sunday, "A Prairie Home Companion" will be repeated at 1 p.m. The original time is still 6 p.m. Saturday. Vietnam Report

Larry Matthews of WMAL-AM (630) will talk to members of the Vietnamese community next week in a special report, "Hearts and Minds: 10 Years After." The series, marking the 10th anniversary of the end of the Vietnam war, will air at 11:20 a.m. and 4:10 p.m., Monday through Friday, and conclude with a short documentary on Friday. Matthews won a Peabody Award in 1982 for his documentary on Vietnam veterans, "They Served With Honor." Holocaust Remembrance

On April 19, WETA will broadcast "Underground Without Bullets: Cultural Resistance During the Holocaust," a documentary about the artistic outpouring of the camp inhabitants. The show was produced by Sam Edelman and Everett Frost and distributed by American Public Radio. WETA will use a 30-minute segment at noon. More From India

In the wake of the news events in India and the popular treatments of Indian culture on television and movies, WNTR-AM (1050) has added "Sounds of India" to its weekend lineup. The program, produced by the Council of Asian Indian Associations of Greater Washington, will be on Saturdays and Sundays from 5 to 5:45 p.m. for the rest of April. Then it will switch to Sundays from 5 to 7 p.m. Youth News

"Youth Point of View," a show produced by Mayor Marion Barry's Youth Leadership Institute, is now heard on WUST-AM (1120) Saturdays at 8:30 a.m. Tomorrow the host, Norman Nixon, interviews television anchor Renee Poussaint. Datebook

WAMU-FM (88.5) is presenting its Spring Festival Concert, "Bluegrass & Sagebrush," at 8 p.m. tomorrow at Fairfax High School. Jerry Gray will host the evening with the Seldom Scene and Riders in the Sky, and WAMU will air the concert on April 20 at 3:05 p.m. . . . Alan Stivell, the Celtic harpist and recent Grammy nominee, will perform at 8 p.m. Thursday at Georgetown University's Gaston Hall and WETA will broadcast the concert April 20 at 9 p.m., as part of its fund-raising campaign . . . Jon Murphy of WBMW-FM (106.7) will be the host of the first telethon of the Fairfax Symphony Orchestra, scheduled from 1 to 10 p.m. tomorrow and then 1 to 7 p.m. Sunday on cable Channel 30 in Virginia. Planning to drop in are Beverly Fox of WLTT-FM (94.7), Robert Aubry Davis of WETA, Renee Channey of WGMS-FM (103.5), Tom Gauger of WMAL and Walt Starling and John Dowling of WCLY-FM (95.5).