Dec. 21 is a day of shame and humiliation for Americans.

On that date in 1988, a suitcase bomb slipped aboard Pan Am Flight 103 by two Libyan intelligence agents exploded over Lockerbie, Scotland, killing all 259 people aboard and 11 on the ground.Of the dead, 189 were Americans returning home for the year-end holidays. And among the casualties was Pan Am itself. The pioneering overseas airline was forced out of business partly by the disaster.

We should not be ashamed because an American aircraft was destroyed. Terrorists can target a civilian airliner of any nation. But we are disgraced and betrayed because six years later, no serious penalty has been paid by the two Libyans and their master, Col. Moammar Gadhafi.

By 1990, American and Scottish detectives had traced the bomb's detonator to Libyan intelligence. In November 1991 the suspects were indicted by a federal grand jury.

The Justice Department even has a diary showing that one of them had stolen luggage tags from Air Malta, enabling them to place the suitcase on a flight from Malta connecting with Flight 103 in Frankfurt, Germany.

Despite all the evidence and alleged United Nations pressure, the Libyan dictator has refused to give up the pair for trial. He has a good reason: In Libya, agents do not bomb a foreign airliner without Gadhafi's approval.

The case must embarrass President Clinton. For six years the tin-pot tyrant of a country of only 4.4 million people has been thumbing his nose at the "world's only superpower" - and getting away with it.

The president also should be embarrassed by a pledge he made during his campaign to "press the United Nations to broaden sanctions to include an oil embargo" against Libya.

Because he made the promise in writing, Clinton cannot use his all-purpose denial: I never said (or did) that.

As things stand, the U.N. has imposed a few wrist-slapping sanctions on Gadhafi. It has banned air travel to and from Libya and the sale of some petroleum equipment. But Libya gets what it needs through its ally, Egypt, which pockets about $3 billion in aid annually from Washington.

Libya earns some 95 percent of its revenue from oil exports. Clearly, if its oil were not bought by our allies - France, Germany, Italy - it would be out of business and Gadhafi might be out of power.

But they all have excuses for continuing to deal with Gadhafi. For France this is especially cynical: In 1989, Libya bombed France's UTA Flight 772 over Niger, in West Africa, killing all 171 passengers and crew.

If Clinton gave the order, the U.S. 6th Fleet could take out Libya's handful of oil-loading terminals on the Mediterranean in about an hour. But the president will not take military action without permission from Boutros Boutros-Ghali, John Major, Francois Mitterrand, Helmut Kohl, etc. He won't get it.

Last Dec. 21, Clinton joined family members of victims of Flight 103 at Arlington National Cemetery to dedicate a memorial to those killed. He rightly called the bombing "an attack on America."

One is sorely tempted to say: Mr. President, another year has passed and the attack on America has not been punished.

On the upcoming anniversary, you have to hope Clinton will have the decency to keep his mouth shut.