It was sophomore Philip Mangum's second "Fancy Dress" weekend at Washington and Lee University and he was grinning contentedly as he staggered out of the ice-cold mountain creek to meander back toward the party. A leg was torn from his tuxedo (he was later seen trying to retrieve it from a tree), and his shirt was bright pink from the mixture of grain alcohol and cherry Kool-Aid he'd been drinking.

As Mangum - they used to call him "Moo Cow" Mangum in Montgomery. Ala. - stomped through the crowd, he stopped to wring out his jacket on a couple of Sweet Briar College girls. They giggled, their own lips hot pink from the alcohol and Kool-Aid mix. After all, this was the biggest party weekend of the year.

It was the kind of scene that one generation - people who went to college in the 1950s and early '60s - remember well. It is a phenomenon that many college students in the Vietnam War years thought they would never see again. But in recent years, as national membership in fraternities has risen again, enthusiasm for college-wide parties has grown as well.

Dartmouth's Winter Carnival is one of the best known, but in the early '70s, according to college spokesman James Farley, "There wasn't really a heck of a lot of interest. You could tell by the snow sculptures; there were maybe a half dozen all over the campus." This year there was one in front of "just about every dormitory and fraternity."

"You know, homecomings is popular again," said Jack Anson of the National Interfraternity Conference. "Homecomings were pretty quiet for a while."

Easter Weekend, another well-known college bash, at the University of Virginia, will be stretched to a whole week this April. Along with the parties there will be "cultural activities" although as the editor of the school newspaper put it, "that may be just window dressing."

The essential purpose of a big weekend, as most anyone at Washington and Lee's Fancy Dress would attest, is the partying itself - a relentless, mind-numbing round of dancing, drinking and carousing.

"They work hard as hell and they play hard as hell," said a W%L graduate down from Baltimore. It has become a tradition, almost a credo, at Washington and Lee.

Nowhere, however, have the decline and resurrection of the Big Party been more pronounced. In 1971, '72, and '73 Fancy Dress disappeared altogether, only to come back with resounding success in the last half decade amid a pervasive air of carefully cultivated anachronism.

At the concerts, ball and fraternity parties in Lexington last weekend, it was still 1963.

"It's a sheltered community, always has been," said one old grad. Politically conservative, Lexington has pictures of Robert E. Lee and Stonewall Jackson prominently displayed around town. ("How come there aren't my pictures of Washington?" one date wondered. "I don't know. There just aren't," her escort answered.)

The May Day protest after the 1970 U.S. invasion of Cambodia even hit Lexington. "Students were calling for a strike and protests. No one knew what strike meant," recalls Robert Keefe, a W&L spokesman.

Vietnam politics combined with disputes over rock bands versus soul bands and drugs versus alcohol. Several fraternities hit the rocks along with Fancy Dress.

By 1974, however, the mood in the country and at W&L had changed. Fancy Dress was revived. In 1975, when black tie was made mandatory, it took off, and last year the ball was so crowded it was difficult to move. This year, even though admittance was more restricted, people flooded into a dining hall that was decorated to remind the revelers of Egyptian treasures.

A faculty wife wandered the halls dressed as Nefertiti. "Hometown honeys" and Sweet Briar girls stood in long lines filing past a live camel at the door.

"Oh, isn't he cute," cooed one girl from Tennessee. "That thing's so cold. He wants to be in the desert."

"No, they're mean," said a friend of hers. "They'll throw up on you, I hear."

They were talking about the camel. But later in the evening some of their boyfriends were doing just that. Lowenbrau dark and Lite beer were flowing freely, as the old Duke Ellington band played into the night. Cups crunched underfoot while boys and girls danced a modified jitterbug, wherever they had room, spinning and twirling through movements called "pretzels" and "dips."

To the extent that they ever went away, the old fraternity traditions have come back strong. It has been only a couple of years since the men of Sigma Alpha Epsilon rolled their piano onto the street and burned it. (Unfortunately for them, their house is across the street from the Lexington police station.)

Last year during the grain alcohol party on Fancy Dress weekend a student-drove his car through the wall of Zollman's Pavilion, the tin shack where bands play. Several months ago a fraternity pledge who went to a party wrapped in cotton was accidentally set on fire.

Washington and Lee is one of the last all-male colleges in the country, and girls who come there for parties are put up in motels and boarding house.Some are known among some of the students as "rack dates" because they sleep with their boyfriends. One fraternity gave the "Golden Brick" award to a member last Sunday, "for total get none for the whole year, y'know."

There is, as an alumnus put it, "a constant striving for conservatism" to W & L.

"It's very country-club oriented," said Scott Franklin, class of '77, as he surveyed the thousand or so grain-drinking students and alumni around Zollman's Pavilion Saturday afternoon. "I think it's their way of maintaining the upper middle class status quo. They come from Highland Park in Texas, from Westchester County in New York, from Roland Park in Baltimore, where I come from."

Half of the 1,350 W&L undergraduates come from private preparatory schools and there is a kind of "preppy" uniform around campus of khaki pants, Topsider shoes and narrow lapels and ties. "Everything comes from Brooks Brothers or L. L. Bean," said Franklin.

In the midst of all this wealth and assurance is a kind of conspicuous waste that sometimes culminates in the big weekend.