These are bad waters for anyone in pinstripes. There are other New England sharks besides the mythical Jaws of Amity. Fins have been sighted near Fenway on the Charles River.

The New York Yankees, champs of baseball, are hemorrhaging here. The pearly white teeth snapping around them on these moon-bathed summer nights at Fenway Park belong to the rapacious Boston Red Sox.

The Yanks should be forgiven if they look backward to see if anything with tills is gaining on them. The Red Sharks' motif surrounds them.

The champs were greeted in their hotel lobby this morning by a New York Daily News cartoon of an unwary Yankee water skier about to be devoured by a Bosox shark. No sooner did the New Yorkers step outside than the real "JAWS 2" poster faced them from the movie marque across the street.

"Gulp," said Reggie Jackson, trying to laugh.

For the Yankees, the third week of June a year ago was the original JAWS - the nonpareil "Boston Massacre." Jackson and manager Billy Martin battled in the dugout, while the Bosox bashed 16 homers in a three-game sweep.

Now, the Yankees wish those good ol' days of dissension and humiliation were back. Then, they were haughty, hated and healthy. Now, they are injured and insecure.

The word, is out in the American League: "The Red Sox clearly have the best talent," says star California pitcher Frank Tanana. "Somebody better stop Boston . . . and fast."

Last year when Boston won the first round of this Back Bay shootout, 10-4 with six homers, the Yankees were furious, because they believed they were better.

On Monday when Bostn won the opener of this series, which has fans lining up for bleacher tickets each day before sunrise, by the same 10-4 score - this time scoring six runs in their last at-bat - the Yanks were subdued.

"If Boston keeps playing like this," said Jackson, "even Affirmed couldn't catch them. We'll need motorcycles . . . but even if maybe we can't catch them, we'll try until time runs out."

A year ago, the Yankees' only enemy was themselves. Their turmoil was internal, intangible. Their baseball fate - by raw force of talent - was always contained within their own locker room walls.

Now, the Yankee burden is both external and tangible. "They're hot and we'r hurt," is the way Graig Nettles capsulizes it.

Seldom has a defending champion entered a crucial period so weakened.

Mickey Rivers, the Yank feared most by Boston, went on the 15-day disabled list (hairline wrist fracture) on the eve of action. Rivers presumably will miss all of these seven midseason showdown games in the so-called 16 Days of War.

In addition, keystoners Willie Randolph and Bucky Dent are hobbling from leg injuries. Thurman Munson's chronic squatting pains (knee cyst) force Cliff Johnson, a defensive butcher, to catch too frequently. Jackson is slumping.

But those are tiny cosmetic woes compared to Martin's real nightmare - a pitching staff that has gone from terrifying to tatterdemalion.

The Bronx starters for this series - Ken Clay, Don Gullet and Jim Beattie - have four wins this season, while Boston's opposite numbers - Luis Tiant, Mike Torrez and Dennis Eckersley - are 22-4.

Because Ron Guidrya, the Yanks' brilliant young ace who is 11-0, requires four days rest, Martin is stuck with a five-man rotation. That means that after Guidry and steady (7-5) Ed Figueroa (still feuding with Martin), the skipper must choose three starters from this collection.

Gullet (1-0) and Andy Messersmith (0-1), both costing the Yanks a free-agent bundle, both perpetually injured.

Clay and Beattie, both tall young right-handers with limited raw stuff and no experience.

Veteran Dick Tidrow (3-4, 4-21 ERA)inning journeyman.

Catfish Hunter, just off the disabled list, sits in the bullpen, his career down to its sad dregs.

New Englanders can't forget that in 60 seasons since Babe Ruth was traded from Boston to New York, the Yankees have been world champions' 20 times, the Red Sox never. The Yanks are the team New Englanders live to hate.

Nevertheless, Bostonians gradually are beginning to realize that their '78 Sox may be the favorite in this match. Yankee age and injuries, plus Boston free-agent spending and wise trading have shifted the balance of power.

The box seat singers at the Fens serenade Martin nightly with "Goodbye, Billy. We hate to see you go." The bleacherites, who start forming their daily ticket line at 5 a.m., chant obscenities at Jackson.

Those two contrasting symbols of the Bronx Bickerers of '77 do not answer in kind. Martin still greets the picadors of the press with, "Where'd you guys come from? Under rocks?"

Otherwise, Martin is tamely out of character here. He caught Boston third baseman Butch Hobson as he was tumbling into the Yankee dugout chasing a pop foul. Of right fielder Dewey Evans' magnificent throw to third to kill a Yank rally, he says, "Some play, huh?"

Asked why Jackson was barreling toward home while new Yank Gary Thomasson swung away, Martin fessed up meekly: "He missed the squeeze bunt sign."

Martin threw a bat-and-glove-hurling tantrum Sunday in New York after Figueroa - order to give a semi-intentional walk - served up a game-losing gopher ball. But Martin has sheathed his sword here in enemy territory. This is not the locale for showing one's vulnerability.

The Best Team Money Could Buy ain't as interesting as it used to be. No pitcher complains, because any healthy hurler is ushered forthwith to the mound. With Rivers sidelined, any outfielder with a live bat will play, with Rawly Eastwick traded and Tidrow starting, Sparky Lyle and Rich Gossage get plenty of work.

Martin, his eye on an eventual Yankee vice presidency, holds his tongue toward owner George Steinbrenner, while the boss, temporarily contented by his World Series ring, has not tampered too much in Billy the Kid's domain.

The Yankees, riddled with traditional baseball problems, appreciate the irony that they are the team - for the time being - with only a normal amount of internal squabbles, while the dirty laundry of the Red Sox is drying in public.

"Bill Lee and Don Zimmer are ripping each other in public," said New York's Nettles. "I don't like it.

"I've seen this movie, I think. Don't the bad guys win?"