Today was the day the U.S. Naval Academy and St. John's College, odd-couple next-door neighbors for 148 years, buried the hatchet and replaced it with a mallet.

Buoyed by seemingly endless streams of champagne, beer and gin-and-tonics, the Middies and the Johnnies converged on a bright green lawn and whacked away at their substantial differences. From the confusion emerged a winner and new national intercollegiate croquet champion, St. John's, but Navy public affairs officer Ken Pease would insist afterward that "everyone won."

When Pease graduated from the academy in 1968, the nation was divided and so were the two schools over the merits of the Vietnam War. The Mids had to change their parade route to the football stadium to avoid brickbats tossed their way by the resolutely liberal Johnnies.

Today, by contrast, Mids and Johnnies frolicked happily in their first athletic/social collaboration in almost half a century, except for a few chess games. It also was the first intercollegiate athletic event at St. John's since 1939, a watershed so lightly regarded that the college athletic director didn't bother to attend. The croquet match was the tongue-in-cheek brainstorm of a St. John's freshman stuck for a story when he was named the school newspaper's croquet correspondent. He challenged Navy, and Navy "never turns down a challenge," said its hastily appointed team captain, Rhodes scholar Mark Hagerott.

So the Mids arrived at St. John's on schedule this afternoon, decked out in dress blue blazers and perfect white slacks, white shirts, white shoes and white straw boaters.

"Those boys are so cute," remarked St. John's junior Chalayne Elias. "Uniforms just do something for me."

The competition wore standard-issue undergraduate funk, mostly Hawaiian shirts and Aussie hats.

Whacking out the first ball was retired Adm. James B. Stockdale, holder of the Congressional Medal of Honor and the Navy's highest-ranking prisoner of war during Vietnam, where he spent 7 1/2 years in captivity. Stockdale graduated from the Academy in 1947, but said he couldn't really remember a thing about neighbor St. John's from those days.

Surrounding the two pitches on which matches were played simultaneously by teams of three per side was a baffled but cheering crowd of about 1,000, half in Navy blue and most with libation in hand. Mayor Richard Hillman appeared, dressed in 18th-century garb in honor of the city's spring festival, which was under way downtown.

"I was afraid the crowd was in an ugly mood," said the mayor, "but then I realized it was just an ugly crowd in a good mood."

As he spoke a roar went up, but it turned out to be obeisance not to athletic excellence but to a giant Budweiser ballon that swept overhead and quickly passed out of sight while the Mids chanted, "Bud, Bud, Bud, Bud . . . . "

"It's a hot-air balloon," explained the mayor. "The city aldermen spent the morning down at the City Dock blowing it up."

The games progressed smoothly, well lubricated by frequent visits to the players from waiters bearing champagne, gin and beer. The drinks eventually had an effect on the players, who grew bolder if less accurate in their shooting.

"Is there always so much drinking?" a visitor asked St. John's sophomore Steven Werlin, who was awaiting his turn to play.

"I don't think there's any other reason to play this game," said Werlin.

In truth, the deck was stacked against Navy. Though it had 4,500 Mids to choose its squad from against only 413 Johnnies, and though Navy's intercollegiate athletic program is a big-money operation with 34 varsity sports against St. John's none, there simply is no croquet at the Academy.

At St. John's the game is something of a passion. To provide a low-key respite from the demanding curriculum of four years of great books, the school has three sets of mallets, wickets and balls always on hand, free for the taking from the library. There's even an appointed "Imperial Wicket," sophomore John Ertle, who oversees the croquet program and who actually knows the rules.

The Naval Academy went in wild pursuit of a few wickets and balls to practice with when the challenge came down last month.

In practice, "We were going to have a cannoneer shoot off a round every time we went through a wicket," said Commodore Bud Edney, commandant of Mids, "but we never could find a wicket."

Final score: St. John's 2-0. But the Mids no doubt will be back.

Said Edney, "We hate to lose."