The cowardly lion is whimpering again.

Congress is looking to President Reagan to free it from the snare it created in 1973, the War Powers Resolution, which allows it to take part in foreign policy decisions and requires it to share the blame.

Ever since four Marines were killed in Lebanon, members of Congress have been hoping that Reagan would acknowledge their existence by honoring the existence of the resolution, all the while signaling that they will not interfere with him in Lebanon.

Sen. Charles McC. Mathias Jr. (R-Md.), one of the authors of the War Powers Resolution, proposed to let the president keep the Marines there indefinitely, once he admitted having sent them to a scene of "imminent hostilities."

In a similar mood of conciliation, brought on by the martial mood occasioned by the South Korean airliner incident, House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) proposed that the president be allowed a grace period of 18 months.

O'Neill took back his proposal when the hawks in his flock descended on him in strenuous opposition. Rep. Samuel S. Stratton (D-N.Y.), one of the foremost advocates in the House of military action, said that Marines' lives were in danger in Beirut for no purpose.

In light of the casualties, 28 other Marines have been wounded, the insistence of the president's men that there are no "imminent hostilities" is farcical.

But any port in a storm when prerogatives are threatened, and White House spokesman Larry Speakes is still saying that there is no "ongoing war" in Lebanon, although U.S. warplanes have begun to gyre on Syrian and Druze positions in the Chouf Mountains.

To the ruination of his presidency, Lyndon B. Johnson waged war in Vietnam without congressional authorization. Despite the precision of the Constitution on the point--"the Congress shall declare war," Johnson held that the Gulf of Tonkin Resolution gave him all the authority he needed to bomb and to escalate and to send thousands of U.S. troops into the jungles.

Congress, which by that time was being bludgeoned by its constituents to do something, finally passed the War Powers Resolution in 1973. Reagan said it's unconstitutional. We hear in his words the echo of Johnson's lament that Congress has tied his hands.

The debate over the War Powers Resolution has served a useful purpose for WHO, ME? Reagan. It has obscured what should be a debate over why we are in Lebanon and how long we intend to stay.

Some Lebanese-Americans, such as former senator James G. Abourezk (D-S.D.), say they believe that Reagan could use the Marine force to advantage by threatening to withdraw it if Lebanon's president, Amin Gemayel, does not go to the negotiating table promptly. Abourezk said he thinks that the trouble is political, that a minority party, the Falange, has taken control of 90 percent of government posts, and that peace would bring a redistribution of power.

But others think that the trouble is religious, the result of an irreconcilable conflict between Christians and Moslems. They see Lebanon as another Northern Ireland, where ancient and nurtured hatreds are so deep and bitter as to be beyond remedy.

If Congress really wanted to exercise its authority, it could hold hearings and ask representatives of the Druze, the Maronite Christians, the Suny Moslems and the Shiites to come and tell us what it is all about.

The debate over the War Powers Resolution is, nonetheless, important and worthwhile. Senate Democrats, who have shown considerable spirit, want to make some kind of a showing to ensure that Reagan doesn't back us into a combat role in Central America while no one is looking.

The outcome the United States desires in Lebanon may be unattainable, but at least it is worthy: we are trying to stop a war.

In Central America, our goal is both unattainable and unworthy. In the interests of "stability," we have financed dubious elements to wage war against the government of Nicaragua, which displeases us.

Although we say we want negotiations, no action or development suggests that we mean it. Last week, the Salvadoran rebel spokesman, Reuben Zamora, was denied a passport.

And according to a top Pentagon official, our malign intervention has only begun. Defense Secretary Caspar W. Weinberger's deputy, Fred C. Ikle, made a startling speech in which he baldly stated that, "We do not seek a military defeat for our friends . . . . We seek a victory for . . . democracy." In this case, "democracy" means the government death squads that murder civilians in El Salvador.

Nobody at the Capitol or the White House knows what to do in Lebanon. If we don't withdraw our forces, we may have to double them.

But many members of Congress know exactly what not to do in Central America, which, dismayingly, is where the real test of the War Powers Resolution may occur.

In Mary McGrory's column yesterday the position of Sen. Charles McC. Mathias Jr. (R-Md.) on the duration of the stay of U.S. Marines in Lebanon was misstated. He proposed to limit their stay to six months.