About 30 striking major league umpires, joined by members of sympathetic local unions, picketed Three Rivers Stadium today and sought to persuade fans to support the umpires by boycotting the Pittsburgh Pirates' game with the St. Louis Cardinals.

Despite sunny weather and a helmet day promotion, the game drew only 10,940 paid. Last year's promotional days averaged 20,000. A Pirate spokesman said there were 459 noshows.

There was minor violence. Pirates officials said car tires were slashed and antennas broken.

A team spokesman said the umpires were not involved in the violence.

Senior National League umpire Ed Vargo and Richie Phillips, attorney for the striking umpires, said the umpires would return to Three Rivers Sunday and a similar demonstration would be staged at Boston's Fenway Park.

Vargo, the plate umpire when Sandy Koufax pitched a perfect game in 1965, wore a "Baseball Unfair to Umpires" picket sign as he chatted with supporting Teamsters from Local 249.

"The union people and the umpires are telling people to stay away from the ballparks," Vargo said.

Though venders, ground crew workers and other union people crossed picket lines, labor leaders lent their organizations' moral support to the umpires, who are holding out for higher pay.

Bus and taxi drivers, who normally make stops along the stadium's inner circle, bypassed picket lines, letting passengers depart along an outer route.

In the fifth inning, a plane carrying a banner, which read, "Baseball is Unfair to Labor," circled over the stadium.

International League umpire Lanny Harris and three sandlotters, some with minor league experience, worked the game.

Pickets passed out leaflets depicting an amateur ump calling a batter out on a pitch that bounced in front of the plate.

"Steeerike 2! Yer out!" the caption said.

Vargo said he knows Harris and the other three umpires who worked the game, Joe Schratz, Ron Houston and Harry Smail.

"Yes, I know those scabs," Vargo said. "They were my friends-no more," he added.