A soft and ample paunch thrust pugnaciously over the armrest of my seat on Ronald Reagan's campaign plane. It belonged to the governor's longtime aide and corny, Lyn (ofziger, who has the permanently disheveled look of a Bowery bum.

"Do you know what I'm doing?" he asked. "I'm having a good time and I'm drinking."

He was, indeed, deeply -- from a large glass of the Bombay Gin that United Airlines has stocked for his personal comfort.

This was not at all the atmosphere of gloom, even despair, that reportedly has shrouded the governor's campaign of late. Nofziger was exuberant.

"We've got the White House on the run," he said. "We hit them on the Middle East last night. Then before they knew what to say we hit them with the 'stealth bomber.' Those a ------- don't know where to turn."

It had been a remarkable day during which Reagan, far from blundering, had shown his prowess as a powerful stump speaker. At noon on Thursday, he gave a rousing anti-Carter speech to businessmen in Jacksonville, Florida, then flew through an electrical storm to New Orleans where, on the creaking deck of a Mississippi paddle steamer, he gave another stirring oration.

At New Orleans airport, the governor loped athletically down the aircraft steps, to be greeted with the surprising news that he had suffered a heart attack en route from Jacksonville.

His phantom heart attack began, it seems, when a woman phoned the radio station WMIF in New York with the bad news, then hung up. Although Wall Street experts believed it was the work of a speculator, Nofziger had a different interpretation.

"I'll tell you who started it," he said. "The White House. Now, I'm going to start another rumor. Write this down. Jimmy Carter has the clap." g

All this raucous, almost barroom ggod humor cannot mask the fact that Reagan's campaign, if not his heart, is suffeirng severe palpitations.

After his nomination as Republican candidate in July, he was leading President Carter in the polls by a healthy 45 to 31 percent. Then the gap closed with Reagan 39 to Carter's 38. The challenger intended to surge ahead in the final two months of the presidential race with a frontal attack on Carter's vulnerable record.

It did not work out quite like that. To Reagan's fury, the newspapers were filled with his own indiscretions and "misstatements" on China, Vietnam and the Ku Klux Klan.

A current joke about Reagan's perofrmances goes: "Today Ronald Reagan issued a clarification of yesteraday's apology for his misstatement the day before."

As his former campaign manager, John Sears, said: "If you are making your opponent the issue, then you should not be spending most of your time explaining why you are not an idiot."

Most of Reagan's aides -- Nofziger, Ed Mese, who runs the campaign, Bill Casey, the chairman, and Mike Deaver, another top man -- are cronies from his California days. Then there is Richard Allen who is favored to be national security adviser in a Reagan administration.

Allen is intelligent and hardworking. Last week he crafted two excellent Reagan speeches. Unlike the others, he has had Washington experience. He was President Nixon's deputy assistant for international and economic affairs and held a senior position under Henry Kissinger on the National Security Council.

Late on Thursday night, in the campaign bus on the way from Dulles Airport, Allen told me how both he and the governor had been misunderstood, especially by the British press, whose coverage of Reagan had been, he said, immature. "The correspondents have not sent full and accurate reports of Reagan's speeches back to their head offices," Allen said. "That means that the British editorial writers only have caricature impressions. You may quote me -- if you do so accurately."

Allen also said the British press portrayed Reagan as a cowboy, using photographs from his old films. That, he said, is a disgrace. In June, Allen met British Prime Minister Margaret Thatcher, who he said showed a deeper appreciation of the governor's finer points.

At last, on Thursday, the Reagan campaign slogan, "The time is now," proved to have some validity. His blistering attack on the Carter administration for leaking highly secret details about the Stealth radar-resistant aircraft for political purposes grabbed the headlines and put the president on the defensive. The continuing investigation into the link between Libya and the president's brother, Billy, fed the Reagan offensive and there were just bonuses to the Republican challenger's central attack on Carter's mismanagement of the economy.

The ebullient Nofziger even doubted whether the Reagan goofs did any damage.

"The conservative Reagan constituency -- and that's not small -- got worried when moderates like Bill Casey, [former U.S. ambassador to Britain] Anne Armstrong and [george] bush took the leading roles in the campaign," he said. "They wondered where Reagan was going. They liked those remarks about Vietnam, evolution and the Klan. It was like revaccinating the Reagan constituency. The media might write us off, but wait and see.

"Let's drink to that."