Ron Kittle's days as a Baltimore Oriole, apparently numbered for some time, officially ended yesterday when the club announced it would not exercise the option on his contract for 1991. Kittle, obtained July 20 from the Chicago White Sox in exchange for Phil Bradley, batted .164 in 22 games, with three RBI.

To have both newly acquired Dwight Evans and Kittle would have been a "duplication" of right-handed hitters, according to Orioles General Manager Roland Hemond, who said a groin injury suffered by Kittle in his last game with the White Sox "hampered" him with the Orioles. Recent efforts to trade him failed.

In another move yesterday, the Orioles acquired left-handed pitcher Paul Kilgus, 28, from Toronto for right-handed pitcher Mickey Weston, 29. Kilgus will be added to the Class AAA Rochester roster.

In 1990, Kilgus appeared in 11 games for Toronto (0-0, 6.06 ERA in 16 1/3 innings) and had the fifth-best earned-run average in the International League (2.84) while going 6-8 in 20 games (17 starts) for Syracuse. He also has pitched for Texas and the Chicago Cubs, and has a major league record of 20-32 (4.30 ERA).

Weston was 0-1 (7.71 ERA) with the Orioles in nine games. He was 11-1 at Rochester with a 1.98 ERA. . . .

Brett Butler, a new-look free agent not wanted by his old team, the San Francisco Giants, has agreed to a three-year contract with the Los Angeles Dodgers worth approximately $10 million.

The Dodgers did not announce the signing, but Butler confirmed it from his home in Georgia.

"I've got to say it was probably one of the hardest decisions I've had to make in my life," Butler said. "I've always wanted to play for the Dodgers."

Atlanta and the Boston Red Sox also had pursued the outfielder. . . .

Second baseman Marty Barrett, who had said he wanted an opportunity to play with another team, has it, now that the Boston Red Sox have released him.