Sensible people, meaning those people who live beyond the Washington Beltway, often ask a sensible question: How in the world, they wonder, can Congress run up a deficit of $200 billion in a single year? An answer of sorts may be found in the tale of the flatulent cows.

It is a mystery story. It qualifies, indeed, as an old-fashioned whodunit, but it is not fiction. At high noon on Saturday, Oct. 27, the last day of the 101st Congress, the Senate completed passage of the Clean Air Act. By a vote of 89-10, this well-intentioned and fearfully expensive legislation went to the president.Buried deep inside the bill was a remarkable provision. The bill authorizes a three-year study of the methane emissions from the flatulence of cows and other ruminant animals. The study is estimated to cost $19 million.

Now, methane is no joking matter. Considerable evidence suggests that methane emissions contribute to global warming. Most of these emissions come from natural sources, such as swamps, marshes and coal deposits, but large amounts also originate in paddies and feedlots.

During debate on the Clean Air Act, the Senate was told of nine recent studies of global methane, including methane emissions from cattle. At least a dozen federal agencies are studying methane in one way or another. The new farm bill directs the Department of Agriculture to coordinate these disparate efforts.

The specific $19-million, three-year study of ruminant flatulence first appeared when the Senate's version of a Clean Air Act was being debated last spring. Who sponsored the provision? No one seems to know. At least no one will say. Manifestly some senator requested it, or some staffer typed it up. In any event, Idaho's Sen. Steve Symms found out about it. He offered an amendment to strike the provision from the clean air bill, and out it went.

That was not the end of the matter. The farm bill came along in midsummer, containing a section on global warming, and behold! There again was a provision for studying the flatulence of cattle. Symms again tried to eliminate the provision. He failed, but the bill went to conference with the House and the provision was abandoned there. Pat Leahy of Vermont, chairman of the Senate Agriculture Committee, said that if everyone continued to treat the authorization as a joke, it wasn't worth fighting over.

The study of ruminant methane now had been killed twice. Some things refuse to die. On Oct. 27 the Senate took up the conference report on the Clean Air Act. Behold! There it was! Symms was aghast. The Senate had voted unanimously to kill the proposal. The House never had considered it at all.

"I do not know how these things happen," said Symms, "but it is here. It is in here, Mr. President. It just amazes me. I see that some extraordinary, tenacious person has once again inserted the study of `an inventory of methane emissions associated with livestock production.' How did it get in there? It is an outrage and all senators should be outraged about it."

Alas, no other senators appeared the least bit outraged. Max Baucus of Montana responded briefly that House conferees had insisted on the study, and "we felt it made sense to finally acquiesce."

The debate went off on acid rain, clean coal and ozone protection. Senators made gassy speeches praising the leadership of other senators. Not another word was said about the flatulence of cows.

Symms managed to insert in the Congressional Record a letter from M.A.K. Khalil, a professor of environmental science and atmospheric studies at the Oregon Graduate Institute of Science and Technology in Beaverton. The letter was dated Aug. 28. He had heard that Congress was considering spending large amounts of money to study methane production by cattle as this relates to global warming.

"In my opinion," said the professor, "such money will be completely wasted. Even if the emissions from cattle could be controlled, it would have no practical or perceptible effect on global warming."

There it stands. How does Congress manage to roll up such monstrous deficits? This is how. The deficits result from an attitude - from a kind of sublime contempt for the taxpayers whose money the members are spending. Until that attitude changes, the deficits will mount. Tuesday's elections will not affect the attitude at all.