WASHINGTON -Since that memorable August moment when George Bush made of Dan Quayle a gift to the country, the question has been: Can Quayle, who seems so energetic in body and so indolent in mind, temper his enthusiasm with lucidity?

The answer came when Quayle clambered onto the Omaha stage with a cutlass clenched between his teeth, eager to shed blood and vindicate Bush's nomination of him.Did he prove himself presidential? No. He stayed in step with the top of the ticket. Quayle touched on - no, tromped on - the Bush campaign themes.

Having had the audacity to begin his most curdled stuff (about how Dukakisites despise the common sense of Midwestern grandmothers and sneer at the idea that America is the envy of the world), it is a wonder that Quayle had the sense to stop. Stop he did, but not before confirming the suspicion that his conservatism is less a creed than an absorbed climate of opinion, absorbed in a golf cart.

As late as 1896, McKinley spent the autumn on his front porch, refusing to campaign because speaking involved an unpleasant undertaking: "I have to think when I speak."

Most of today's candidates recognize no such requirement and are emancipated by public tolerance from any such expectations.

It was not surprising that Quayle was not smooth as silk, or even as polyester. And Bentsen was unusually awkward when recurring unnecessarily to his "breakfast club" fund-raising, and when lamely defending it as "legal."

Then Bentsen with the syrup of his voice seasoned with vinegar, said Quayle is no John Kennedy. (Quayle had said that he has as much experience in Congress as Kennedy had when he ran for president.) Then a questioner made a point that Quayle was perhaps too stunned to make: Quayle is running for vice president with more experience than Bentsen had when he ran for president in 1976.

Bentsen's performance in Wednesday's debate was, on balance, sufficient to establish him as the most presidential of the four men on the two tickets.

He gave Dukakis a lesson in how to cope with the Democrats' intractable problem -prosperity. Looking like a 19th-century mural of Integrity Reproving Folly, Bentsen said, in effect: Seventy months of economic expansion? Of course. Any fool can slash taxes, give the Pentagon a blank check, finance it with $200 billion deficits and wind up with economic stimulus.

But we are storing up trouble down the road. And meanwhile Reagan's deficits - it took him less than five years to double the national debt - is costing every American man, woman and child $640 a year in interest charges.

Three opportunities were not enough for Quayle to come up with a counterpuncher's answer to the question, What would you do first if you had to replace President Bush?

The answer is: I would continue with the Bush policies because I agree with the man at the head of my ticket, which is more than Bentsen can say.

Let's be blunt. If Bush is elected, Quayle will not matter as long as Bush has a heartbeat. Quayle will not be trusted to handle even the more serious foreign funerals.

If Dukakis is elected, Bentsen will matter because Dukakis knows next to nothing about Washington, or national security, or about how little he knows.

If Dukakis wins, the crucial question will be: How good will he be at changing his mind? If the education of Dukakis becomes necessary, Bentsen had better be nearby.