The contract for Cito Gaston, who has led the Toronto Blue Jays to consecutive World Series championships, was extended through 1996, after which, he said, he probably will retire. . . . Outfielder Kevin McReynolds, bothered by a bulging disk in his back, was put on the 15-day disabled list by the New York Mets. . . . The New York Yankees activated relief pitcher Steve Howe from the disabled list.