Vice President Bush has been thumbing through dictionaries in search of a definition of "shame." Maybe he'd like a little help.

Shame: a feeling of having lost the respect of others because of improper or incompetent conduct, as in the administration's cozying up to the racist regime that Bishop Desmond Tutu has just won a Nobel Peace Prize for resisting.

Shame: an embarrassment, as in the expectation that the doctrine of "constructive engagement" would lead South Africa to mend its racist ways.

Shame: something regrettable or unfortunate, as in the defeat last week of a bill -- opposed by the administration -- that would have reduced a little this country's support for South Africa's apartheid.

The last, particularly shameful, example of the definition cannot be laid to the administration alone. It had plenty of help from Congress, which could have served the interests of international justice by making clear that America could no longer be counted on to underwrite apartheid.

First, the House dropped a provision proposed by Rep. William Gray (D-Pa.) that would have banned new American investments in South Africa (including bank loans to private parties) and also barred the importation of South African krugerrands. The bank-loan provision alone would have been highly significant, considering that some $4 billion in bank loans are outstanding.

A compromise engineered by Rep. Stephen J. Solarz (D-N.Y.) dropped the krugerrand proposal and banned bank loans only to the South African government and its entities -- currently less than $400 million -- and called for voluntary compliance with the Sullivan (fair employment) principles. The compromise, an amendment to the Export Administration bill, was accepted in House- Senate conference, and there was reason to believe that it would be enacted (even though members of the Congressional Black Caucus refused to support it as too weak).

But during the maneuvering in the week before adjournment, word circulated that the administration would not accept the bill with the bank-loan provision in it. At the end, the whole Export Administration package was killed -- allegedly by Republicans wanting to spare the president the embarrassment (shame?) of vetoing the South Africa sanctions at a time when he was preparing to debate challenger Walter Mondale on foreign policy.

Sen. Jake Garn (R-Utah) denies that report. "The final conference bill had a lot of provisions that we were opposed to, though we also opposed mandatory sanctions against South Africa," Garn said in a telephone interview from Salt Lake City. "The administration never said to me that they would veto because of South Africa alone."

Democratic and Republican staffers who were party to the negotiations have a different recollection, but no matter. The South African economy is heavily dependent on American support, a fact that gives the United States considerable leverage in nudging that country toward racial justice.

Disinvestment, the idea favored by South Africa's staunchest foes here, probably couldn't pass Congress. Some anti-apartheid partisans think it shouldn't, since it would constitute an all-or- nothing tactic that would remove U.S. influence and perhaps even leave South Africa's blacks worse off.

The beauty of the Gray proposal was that it would have put South Africa on notice that the United States meant business, and it would have implied a programmed tightening of the economic screws, perhaps leading even to disinvestment, if South Africa remained unresponsive.

Even the considerably weaker Solarz compromise would have been helpful. But the Reagan administration, as it has done right from the beginning, offered no assistance -- only opposition to any measure with any hope of moving South Africa away from its racial intransigence. "Constructive engagement," the obviously failed notion that Pretoria will be more responsive to warmer treatment than to actual or implied threats, remains the administration's policy.

And that, Mr. Bush, is a shame.