Songwriter Jimmy Buffett, the patron saint of sun-slick boat decks and of the one-two punch-drunkenness of the hammock's sway and lethal tropical drinks, is stretched out high and dry on a couch in the Watergate Hotel. His left leg is encased in a plastic mesh cast like a toothpick swathed in rumaki. From far off on his personal horizon, his toes wriggle forlornly.

"When this come off, I'll be the happiest man in the world," he says fervently, ". . . but it's probably added five years to my life."

Three months of enforced physical calm is a far cry from the 280 days every year Buffett used to spend on the road, parlaying his visions of the Key West good life into a reputation as a high-energy club performer. While the Eagles were mapping out the neon geography of Southern California, and Bruce Springsteen was throwing a half-light on the alleys of New Jersey, Buffett was rediscovering the lost treasures of a latter-day pirate's existence.

Key West, in Buffett's songs, is a sunny, funny spot where the inhabitants are "more than contented to be livin' and dyin' in three-quarter time," "wasted away again in Margaritaville." His characters are smugglers and dope dealers (as he describes himself), fishermen, tourists, carousers and lovers of dark-eyed women. Among their number is the protagonist of what is probably his finest composition, "A Pirate Looks at 40," about the wreckage of a middle-aged anachronism.

About two years ago, Buffett was ready to bolt out of his contract with ABC ("It was an 80-20 split about who was promoting Jimmy Buffett, with me doing the 80"); instead, he hooked up with super-manager Irving Azoff, whose other clients include Steely Dan, Boz Scaggs and the Eagles. Now, he says, "it's a 50-50 deal."

Azoff, whom Buffett calls "the Billy Martin of rock 'n' roll," has taken the weight of day-to-day grinding off Buffett and freed him to profit from his long apprenticeship. "The big break was 'Changes in Latitude, Changes in Attitude' (the album from which came the single "Margaritaville"); the big break was Irving renegotiating my contract."

The commercial success of Buffett's pirate image has given him the means to live like one. He has an apartment in Key West, which is too hot to inhabit in summer, and a house outside Aspen, where his wife, Jane, spends much of her time when the band is on the road. His summer home is his ketch Euphoria II, currently anchored at Martha's Vineyard.In an article written for Outside magazine, Buffett describes the boat as having two air conditioning units weighing 550 pounds, and room for 48 cases of beer, a library of hardbacks, a freeser full of tenderloin, a salon which converts into a dance floor, "and six people not the least bit interested in sacrificing any of those luxuries for an extra half-knot of speed."

He has another "home" in Montana, where his brother-in-law, Tom McGuane "92 in the Shade" and "The Bushwacked Piano" and screenplays "Rancho Deluxe" and "Missouri Breaks") is the common denominator in a Faulkneresque confusion of relationships.

McGuane's neighbors include his first wife, Becky, who is now married to Peter Fonda; poet Richard Brautigan; director Sam Peckinpah, and a host of other artistic types. McGuane met his second wife, Margot Kidder, furing the filming of "92" and he met ex-lover Elizabeth Ashley during the filming of "Rancho Deluxe." His current wife is Buffett's sister, Laurie. Buffett himself, who scored and performed in "Deluxe," used to spend the summers there absorbing vignettes and characterizations.

Nowadays he pals around with other humorists - Hunter Thompson in Aspen, John Belushi (who spent last weekend on the boat) in New York. Their friendship is reflected in his appearances in Outside (owned by Rolling Stone) and on "Saturday Night Live."

His emphasis on humor, as opposed to comedy, is deliberate. A copy of E.B. White's essays lies in his suitcase; in his songs he throws in Steve Martin and Ricky Ricardo and Andy Devine. His flair for offbeat thymes rivals Ogden Nash's - pairing of "Bwana" and "marijuana."

This predilection for humor is a major factor in his reluctance to write while out on tour. "They all end up being road songs. Everybody gets p - y and moany and all the songs sound like that. A lot of disasters strike you on the road, but two days later you can laugh about them. I may take notes, but I don't write until I get home."

This time, the band is on the road until mid-August; then Buffett is off to London (to attend the wedding of his first wife) and Paris (to celebrate his first anniversary with Jane). When he returns, the band will go into a series of small-hall concerts to record a live album.

Satisfied that he has "established (his) credibility" as a songwriter and performer, Buffett would like to stretch out into other media. He'd like to do more articles like the one for Outside (he majored in journalism at Alabama), has three screenplays "on the shelf," and intends to write a novel someday. He also threatens an autobiography - "nothing vindictive, just humorous."

Buffett's broken leg is a trophy from a pick-up softball game in Miami; nevertheless, he and his Coral Reefers went face-to-face with the White House softball team. Buffett's team was short on pitchers ("just like the Yankees") and he, of course, couldn't play third base. Undaunted, he strapped a shinguard over his cast and limped to the mound.Under the bill of his cap, his water-blue eyes were steely. Around his neck hanged the solid-gold anchor he wears instead of a wedding ring. He talked up the infield, he batted with a pinch runner. The White House stomped them, 26-11.

"It'll be funny tomorrow," he says a day later. "It's not funny yet."

He did have his moment of glory. Later that evening, as the National League rose up to squelch the American League in the All-Star Game, Buffett pulled out a major-league baseball jersey, "Dodgers 6" - the uniform of All-Star game MVP Steve Garvey.

Buffett shrugs. "It was the only one in size 38."