SAN FRANCISCO (AP) _ San Francisco rocked again, but this time it didn't take an earthquake. Car horns blared, firecrackers popped and pots and pans clanged as thousands of people spilled into the streets to celebrate the 49ers' fourth Super Bowl triumph in nine years.

The celebration of the 49ers' 55-10 rout over the Denver Broncos began well before the official end of Sunday's National Football League championship contest that was watched by perhaps 120 million Americans.

''This is a Bay-area celebration of life,'' said Leo Bigley, 30, riding in an impromptu parade of cars jamming the Broadway nightclub district.

Another parade was scheduled for this afternoon, after the team returned from New Orleans.

There were no parades planned for Denver, whose Broncos joined the Minnesota Vikings with the worst Super Bowl records - 0-4.

Broncos officials asked that a rally at Stapleton International Airport be canceled, said Brian Muir, a spokesman for the Denver Super Celebration '90.

Some maintained optimism.

''I think the Broncos will be in the Super Bowl next year and they'll probably win,'' Doug Spainhower said at a Denver bar.

Late into the night in San Francisco, there were no reports of celebration- re lated violence such as in 1982, after its first Super Bowl victory.

Police said there were reports of some gunshots being fired in celebration. Dozens of arrests were made, most for minor offenses such as drunkenness.

From atop Russian Hill, yellow headlights and red brake lights moving in opposite directions along Broadway formed a stream of 49ers' red and gold. The lights of the San Francisco-Oakland Bay Bridge, which were darkened more than a month after a section fell during the Oct. 17 quake, stood out in the distance.

''This is doing the city a lot of good. It's helping to put the city back on its feet,'' said Lee Shubin, who added that the victory helped ease the sting of the San Francisco Giants 4-0 loss in baseball's World Series to the cross-bay rival Oakland A's.

''It helped tremendously,'' Bigley said of Sunday's victory. ''The quake happened right during the football and baseball seasons and took the spirit out of it. When the Niners came back, it wasn't hysteria but all felt a commitment to this as a way to show we can rebuild.''

Fans riding in flatbed trucks and hatchbacks blared dance music from boom boxes and leaned out of car windows exchanging high-fives with fans crowding the sidewalks. In some areas, they rocked buses and engulfed cars. About a dozen people rode atop one bus and screamed ''Niners 3/8 Niners 3/8'' A few feet away, an ambulance driver rolled down his window and shook hands with fans.

With four Super Bowl titles, the 49ers have matched the NFL record of the Pittsburgh Steelers, who won their championships in a six-year span ending in 1980.

''They did a perfect job. From the beginning, we knew they would win,'' said Tasi Silifaiva, among a carload of young fans in the Mission District.

''I'm just thrilled, just thrilled. I love them and this city,'' said Rachel Delacruz, who banged a pan with the strainer.

Some San Franciscans, however, were more thrilled to have the streets to themselves during the game.

While her husband was watching the game with friends, Sonja Jones took advantage of the sunny day to take ''the longest bike ride I've ever been on.'' ''The streets were empty. All you saw were big fat men waddling out of bars yelling the score,'' she said. ''I can't understand how these big apes can handle it.''