George McGovern couldn't resist, Vindication was close at hand.

It was Monday night on the tax bill in the U.S. Senate. A coalition of Democrats and Republicans led by Sens. Sam Nunn (D-Ga.) and Lawton Chiles (D-Fla.) had just offered an amendment to cut income taxes by $142 billion so long as the government restrains federal spending to meet prescribed targets.

An impish grin spread across McGovern's face as he recalled all the heat he took in his ill-fated 1972 Democratic presidential campaign for proposing to hand back $1,000 "demogrants" to middle-income taxpayers by means of drastic reductions in government spending. Wall Street had attacked him for offering pie in the sky. Editorialists had ridiculed him.

Now the South Dakota Democrat asked Chiles:

"Do I understand the senator from Florida to say that under the proposal he supports, the average middle-income taxpayers will get an additional $1,000 beyond what they are supposed to get?"

Titters spread through the chamber, but Chiles didn't seem to notice at first.

"I said they would pay $1,000 less than they would have paid," he replied, somewhat cautiously.

"Does not the senator from Florida think that is an awfully radical amendment?" McGovern asked, savoring every syllable.

With loud laughter bursting around him, Chiles agreed. "It is very radical, " he replied.

The amendment was promptly adopted, with McGovern voting a vigorous aye along with 64 other Senate "radicals."

That little playlet was one of many that took place on and off the floor Monday night and again yesterday as the Senate worked its will on the Revenue Act of 1978. Lobbyists in the ornate chamber milled around anxiously all day, seeking to keep or kill some special provision that had brought them to the Capitol.

Even the United Egg Producers showed up, bearing cartons of fresh eggs to advertise their interest. The bill approved by the Senate Finance Committee included a 10 percent investment tax credit for chicken coops, and the egg men were bent on keeping it there."

"We heard Sen. [Edward M.] Kennedy was going to offer an amendment to take it out," said Claude Silva, an egg producer from Turlock, Calif. Gently, Silva and his three colleagues made plain that the phrase "chicken coop" severely understated their economic interest in the matter.

"To us, a 'chicken coop' is 18 inches by 36 inches," he said. "The buildings we put up hold 50,000 chickens . . . they cost $175,000.

"Not including the birds," one of his companions added.

The committee-approved measure was thick with what Sen. William Proxmire (D-Wis.) denounced this week as "the bearded, one-eyed man-with-a-limp" amendments - mostly couched in general terms, but with specific dates and provisions that limit their application to one or a few individuals or companies. Proxmire and Sen. Howard M. Metzenbaum (D-Ohio) served as a sort of self-appointed morality patrol on the Senate floor to protest the addition of any more such provisions, but they faced an uphill battle until the Senate invoked cloture to limit debate and prohibit consideration of the dozens of nongermane amendments awaiting action.

The fate of the "James B. Allen taxpayers' attorney fee award act of 1978" illustrated the turnabout that cloture wrought. It was belatedly introduced by Sen. Jesse A. Helms (R-N.C.) - in honor of the late Alabama Democrat - to bring the Internal Revenue Service to heel for "willy-nilly actions against taxpayers who refuse to knuckel under." The proposal, whose merits no one contested, would make the IRS pay the legal costs of cases it loses.

Helms acknowledged that it was nongermane to the tax bill, but asked his colleagues to remember Jim Allen.

"I know he must be looking down on the Senate and saying, 'Boys, pass this one,'" Helms thundered.

Metzenbaum said he thought the amendment was a good one, but objected to it nonetheless. To Helms' chagrin, it was ruled out of order.

The pace picked up even more speed yesterday with the approach of Yom Kippur at sundown. The five Jewish members of the Senate urged their colleagues to finish as quickly as possible so they could observe the holy day.

But last night's rush on the tax bill could simply drive the unsated interest groups aboard other bills before Congress goes home. Senate Finance Committee Chairman Russell B. Long (D-La.) assured Helms, for example, "that we will have an opportunity to pass other revenue bills before Congress adjourns' and lo, the James B. Allen taxpayers' attorney fee award act of 1978 may wind up on one of them.