Richie Phillips, the lawyer for major league baseball's striking umpires, returned to his Philadelphia office today, but continued negotiating with the two league presidents by telephone late into the night amid reports that both sides had given up on the playoffs yet hope to resolve their differences in time for the World Series.

"We have had many discussions," Phillips said by telephone from his Philadelphia home. "But I'm not going to discuss anything about the details."

Contacted around midnight EDT, he said he planned more talks with Chub Feeney, president of the National League, and Bobby Brown, American League president, again later in the night.

Meanwhile, semipro umpires were assigned to the third games of the National and American League championship series as they shifted sites. In the National League, a four-man crew of umpires from Yuma, Ariz., was hired for tonight's Cubs-Padres game in San Diego.

The four, Terry Bovey, Frank Campagna, Frank Fisher and John Stewart, worked as a unit in spring training "B" games in past years and in 18 regular-season games during the 1979 umpires strike.

In Detroit, where the Tigers will take a 2-0 lead into Game 3 against the Kansas City Royals Friday night, three of the umpires who worked in Kansas City are expected to join three new umpires. Dick Butler, supervisor of American League umpires, said he was unsure today whether former major league umpire Bill Deegan, who worked home plate in both Kansas City games, would continue in that role.

"We may have ridden that horse to death," Butler said. "We told Bill to take a day off and see how he felt. We may give him another day off. It hasn't been decided yet, though."

Little had been decided in the dispute centering on the umpires' demand for an increase in postseason pay and more job security. League presidents Brown and Feeney said they offered a 20 percent increase to the umpires who work the games. Phillips said he wants a playoff pool of money for all umpires, regardless of whether they are assigned to work postseason play.

"I think the umpires want to work the World Series," one baseball official said today. "We certainly want them back so people can focus on the games. But now, maybe they realize, that with or without them, we're playing and surviving."