New York Giants -- Signed C Bart Oates, lately of the USFL Baltimore Stars, who waived right of first refusal in light of the NFL team's offer of a reported $1.1 million over four years, including $125,000 signing bonus; waived C Rich Umphrey.

Indianapolis Colts -- Acquired LB Dave Ahrens from St. Louis Cardinals for a draft pick; waived CB Wyatt Henderson.

Cleveland Browns -- Acquired DE Sam Clancy, the former Pitt basketball player, from Seattle Seahawks for a draft choice.

San Diego Chargers -- Holdout DB Mossy Cade rejected a "final" offer. BASKETBALL

Los Angeles Lakers -- Waived F Jamaal Wilkes, whose scoring average for 11 NBA seasons slipped to 17.9 points a game when he was used in only 42 games for an 8.3 average last season. The Lakers say they will make good fully on his current contract; won't say when it expires. As a free agent, he will be free to negotiate without his Lakers salary affecting his new team's salary cap. BASEBALL

Seattle Mariners -- Put RHP Jim Beattie on 21-day DL, facing right shoulder surgery. BICYCLING

World Championships -- Soviet team won the amateur 100-kilometer open road time trial in Giavera del Montello, Italy. Czechoslovakia was second and Italy, the 1984 Olympic champion, third. HORSE RACING

Spendthrift Farms -- Leslie and Brownell Combs signed a letter of intent to accept a $57 million offer from Ohio and Florida real estate developer Manuel Mayerson for their controlling interest in the 2,450-acre farm, one of the largest and most successful throughbred breeding operations. COLLEGES

Southern Methodist -- Negotiated with the NCAA the severity of penalties to be lodged against a second, unidentified assistant football coach involved in recruiting violations, said Athletic Director Bob Hitch. It will be about the same as the sanctions against the first coach: a one-year ban from off-campus recruiting and 15 percent pay cut.

Missouri -- Senior FB Santio Barbosa, from Oxon Hill (Md.) High School, was one of four varsity players declared academically ineligible for 1985 football.