Georgetown University's basketball team members played with green ribbons sewn onto their uniforms last Saturday to show concern for the 20 young Atlantans who have disappeared over the last 19 months, 18 of whom have been found dead.

"Sometimes we get too involved in our own little worlds," said John Thompson, the Georgetown coach who proposed the idea, "but sometimes it's important to make a statement. It struck me as something we could do."

Radio announcer Robyn Holden was listening to the news on her way to work last Friday when a reporter mentioned the spiraling child death toll in Atlanta. The report haunted Holden until she went on the air on her own show at WHUR radio, and "I just got on the air and asked . . . which of us are sending letters to elected officials to let them know that black people all over the country are not going to view this as just an Atlanta issue, that we're going to stand together all over the country because our children are dying," said Holden.

Her listeners suggested wearing blue and black ribbons -- symbolizing hope for the children still missing and grief for the dead, she said.

With increasing alarm over the unsolved murders of black children in Atlanta, many local leaders and personalities are looking for ways to express their concern for the victims and their families and to prod federal authorities into intervening more extensively in the still-unsolved case.

So, taking a cue from the galvanizing symbol of the yellow ribbons to welcome home the hostages, Washingtonians have been urging each other to wear green, blue, black and red ribbons until the Atlanta murderer or murderers are founds.

"I don't think it makes any difference what color people wear as long as people show concern," said WOL's Bernie McCain, who announced on his Saturday show that the station would begin distributing red ribbons Monday. He chose red, said McCain, "for the blood of the children, the bloody tears of the parents and the anger and indignation felt by the national community" over the delayed, and limited, intervention by the federal government. It was not until Saturday that President Reagan authorized a federal task force to aid Atlanta's investigation of the case.

A Southeast minister, the Rev. Lehman Bates of the First Baptist Church of Marshall Heights, sent a letter to other local ministers two weeks ago, urging the wearing of black ribbons and asking ministers to join a group called United for Survival. Bates' letter recommended a march on the Justice Department in a demand for federal help in solving the murders. The ministers have not taken action.

Taking the Georgetown lead, Lark McCarthy, host of Channel 7's "Morning Break," placed a green ribbon next to her chair on the set Monday, because "green symbolizes life," she said. The ribbon "is there to say, "Remember this case; press for action'" until the station is satisfied that the responsible person or group has been brought to justice, McCarthy said.

McCarthy, like Georgetown's Thompson, chose green because of a newscast of a Philadelphia grandmother who began phoning newspapers and television stations several weeks ago to persuade Philadelphians to start wearing green. The woman, 67-year-old Georgia Dean of Germantown, says she has seen her idea spread to Atlanta, Chicago and other cities.

"I just thought about what I could do in my small, tiny way," she said in a telephone interview.

"I'm so excited about it. I figured nobody cared."