Former President Richard M. Nixon, acting as an arbitrator, decided today that major league umpires should receive a 40 percent increase in pay for working additional baseball games in the two divisional championship series.

Nixon, chosen by baseball Commmissioner Peter Ueberroth to decide the dispute between baseball and the umpires, said in a statement, "The arbitrator's decision is that because the championship series have been expanded by a factor of 40 percent, the working umpires are entitled to receive a 40 percent increase in compensation, which amounts to an increase of $4,000 per umpire, or a total of $48,000 per year for the 12 working umpires for the years 1985 and 1986."

The American and National league series were expanded from best-of-five to best-of-seven, beginning with the 1985 season. The umpires threatened a strike, but later agreed to the arbitration by Nixon.

The statement by Nixon also said that only the working umpires should receive additional compensation for 1985, but that for 1986, an "additional 40 percent increase in the League Championship Series justifies a 40 percent increase in the contribution the leagues should make to the pool for all 60 of the umpires."

That additional amount for 1986 should be $64,000, Nixon said.

The Major League Umpires Association had sought a $5,000 increase for each of the 12 umpires and a $60,000 increase in the umpires' pool.

The presidents of the American and National leagues had offered a $2,500 increase for each working umpire and argued for no increase to the pool.

For the years 1984-86, the current agreement calls for each umpire working the league playoffs to receive $10,000. Nixon said that amount should be increased to $14,000 apiece for next year.

Richie Phillips, general counsel for the umpires association, hailed Nixon's ruling as "another significant advance for the umpires." American League President Bobby Brown described the arbitration decision as a "compromise that did not surprise us and we can certainly live with."