Soon after Interior Secretary James Watt banned the Beach Boys from Washington he was forced to eat crow. Yesterday afternoon at RFK stadium, two Beach Boys fans declared Watt's menu had changed. "Watt Eats Quiche," read the enormous red paint-splashed banner waving lightly in the breeze, a reference to what Real Men are alleged not to do.

This was clearly a Beach Boys-lovin' crowd.

Earlier in the balmy afternoon, more than 50,000 watched Washington's Team America beat Fort Lauderdale's Strikers, 2-1. But after the home-team victory, the rock and soccer fans were getting all their kicks out of California.

Beach Boys lead singer Mike Love generally avoided the topic of Watt's short-lived ban on rock music, mentioning him only once from the stage set in the middle of the stadium. "I thank all you undesirable elements for coming," he shouted, and the crowd roared its approval. "Looks pretty desirable to me."

The attire of the hour seemed to be either Beach Boys T-shirts or flower-printed "surfer shirts." Three young boys paraded through the aisles with plastic flower leis around their necks. Refugees from the '60s, lots of families and little kids eating cotton candy filled the stadium to a crowd that was only 392 short of capacity. Metropolitan police reported no significant violence or arrests.

It was a three-stop day for the Beach Boys, who followed the RFK concert with a White House performance to benefit the Special Olympics and later were to help Vice President Bush celebrate his 59th birthday.

At RFK, three people wore homemade red T-shirts bearing the slogan "I Hate Wayne Newton." Newton was chosen by Watt as this year's July Fourth entertainment on the Mall; two years ago, the Beach Boys drew a crowd of 400,000--a crowd Watt described as containing the "wrong element." "If we had had more room, we'd have added 'and James Watt' " to the slogan on the T-shirt, said David Groves of Washington.

"First of all, it was absolutely asinine to label the Beach Boys as hard rock," said Groves. "All kidding aside, it's another example of some of the things going on with the current administration. It's ridiculous for them to say it brings on the drug scene."

Said Mark Pena, 24, of Maryland, "I felt very offended as a young adult. Watt was using a few unfortunates to represent a larger population that would be at this type of event. The Beach Boys are not the type of band to attract rowdies--they attract music enthusiasts."

Watt "just doesn't understand what's in today's people's hearts," said Shawn Bornington, 26, one of the owner's of the "quiche" banner. "Being here has nothing to do with drugs."

What it seemed to have most to do with was music, like "Wouldn't It Be Nice" and other Beach Boys standards. Nearly everybody was singing along at one point or another, and the crowd was up dancing in the aisles and on their chairs much of the time.

And when Mike Love announced the band would sing John Lennon's "Imagine," the massive stadium was virtually silent.

Said Jane Carney, "This is great, wholesome fun." add e The Concert: Memories Of Things Past

Despite a muddy, muffled sound system and despite a set still dominated by worn-out oldies, the Beach Boys sounded a lot fresher at RFK stadium yesterday than they did in their Washington Monument debacle two years ago.

For one thing, all three Wilson brothers were present for the first time in years. A healthier, livelier Brian Wilson, who wrote and produced all the group's hits, contributed more to the show than he had in the past. Drummer Dennis Wilson gave the music a kick it had been lacking. Carl Wilson led the tightly packed harmony vocals, which once again sounded well-rehearsed and accordingly gorgeous.

Although the Beach Boys have improved a lot in two years, they are still a long way from their past glories or possible potential. Not only did they dwell on their own car-and-surf oldies, they also inexplicably sang oldies by John Lennon, Del Shannon, Chuck Berry and the Del-Vikings. It was no accident that the concert's high points came when the band escaped the past briefly and sang two songs from Carl Wilson's recent solo album. Despite the bad sound and conservative repertoire, the crowd of 50,000 danced until the upper deck began to bounce to the beat.