BEFORE HE does it again, President Reagan might stop and think what effect a new bombing of Libya could have on the forgotten hostages who surely represent the "innocent Americans" for whose benefit he is waging war on Qaddafi.

After the first bombing on April 21, the President received a telegram of congratulation -- one of many, of course -- from Frank Sinatra. It said, "Encore. Encore. Francis Albert."

Mr. Sinatra holds the Medal of Freedom and a high place in the president's esteem, but let us hope that his counsel in this case will not prevail.

When the president told the Chamber of Commerce that he was ready to do an encore over Tripoli if given proof of more Qaddafi evil, he was applauded. The president added that he won't hesitate to hit Iran and Syria, too, if he gets the goods on them.

Most Americans feel awfully good about bombing Tripoli, but before he gives them a chance to feel even better about a repeat, they -- and he -- might take a moment to think about the hostages still being held in Lebanon and the families who dread the ring of the telephone and the evening news.

AP reporter Terry Anderson, Fr. Lawrence M. Jenco, Dean Thomas M. Sutherland of the American University in Beirut and David P. Jacobsen, director of the university's hospital, are still presumably together. Their chances for survival were put in enormous jeopardy by the raid and will approach the vanishing point if the F111s fly again in the Middle East.

To make the point that reprisal breeds reprisal, kidnappers delivered the body of another American hostage -- Peter Kilburn, librarian of the American University -- with a note saying they had shot him in retaliation for the raid.

The message seemed clear enough.

But the American people are not focused on the fate of the remining four.

They never hear about them from the White House, although the president protested at his last press conference that "they've never been out of our mind for a minute".

Unlike President Carter, who wore his hostages like a hairshirt in the last year of his presidency, Reagan has kept his distance from the families of the Americans held in Lebanon. It is not like him. He relates powerfully to individuals in trouble, always seizing the particular over the general. But in this instance, he has reversed himself. He is overlooking the welfare of four known individuals in the interests of unknown Americans who might meet a similar fate.

He never even mentioned the captives until the crisis of the TWA jetliner forced him to. Then he said he would not settle for the return of the 39 from the plane; he wanted all 46 Americans released. (There were at that time seven known captives. Since then, embassy employe William Buckley reportedly has been killed in addition to Kilburn, and the Rev. Benjamin Weir has been released.)

Jeremy Levin, a Cable News Network correspondent who was released after his wife, Sis, went on a goodwill mission to Damascus, says he thinks it is the absence of wives from among those pressing for release that has made the difference.

The president might think about Elaine Collett, the American wife of Alec Collett, a British journalist kidnapped while on a writing assignment for the United Nations. Initially, the body of Kilburn was identified as that of her husband. After Kilburn was determined to be the victim, her husband's captors released a gruesome videotape of a man being hanged. They said it was Collett. She doesn't know.

The president did not call the Kilburn family and made no statement about his death.

The official silence over Kilburn was in sharp contrast to the repeated expressions of sympathy for the murder of Leon Klinghoffer, a passenger on the Achille Lauro which was seized by hijackers in a much-televised crisis of last October.

"We are saddened and outraged by the brutal killing of an innocent American," said the president.

The Tripoli raid, cheered by so many Americans, brought terror to the hearts of the relatives of the hostages.

Says Peggy Say, Terry Anderson's sister, "I don't know whether they didn't think about the hostages or whether they did and decided they might have to be sacrificed in a retaliation. I have never faced the thought until now that Terry might be executed. The president is protecting American lives in the future. Whose life is important?"

David Jacobsen's son Eric, a San Francisco health service office manager, says Reagan "is waging a war which he hopes will save lives of Americans in the future, but there are lives of innocent victims that need to be saved now."

More bombings will bring more death to many Libyans, or even Iranians and Syrians, and may deter tomorrow's terrorists. The four forgotten hostages are Americans. They are innocent. They don't deserve to die one by one, which could happen if Reagan strikes again.