BRIEFLY DONAHUE REPLACES WALSH AS 49ERS GM.

Terry Donahue is general-manager-in-waiting no more.

Donahue, the former UCLA coach, will take charge of the San Francisco 49ers' day-to-day operations from his mentor, Bill Walsh, who will announce his resignation today.

Walsh laid the foundation for the 49ers' two-decade run of success as the coach and general manager from 1979 to '89. Under a new three-year contract, he will remain with the club as a consultant.

Donahue became the Pacific-10 Conference's winningest coach during a 20-year stay at UCLA.

FOOTBALL: The Avengers signed receiver Chris Jackson to a one-year contract, and last year's Arena Football League rookie of the year might play Thursday against the Florida Bobcats.

- Rich Hammond

--Fullback Howard Griffith, a key to the Denver Broncos' rushing attack for four seasons, has signed a three-year, $4.3 million contract with the Broncos. The Broncos also signed free-agent quarterback Steve Stenstrom and linebacker Antonio London.

Other signings Tuesday included six-year NFL veteran quarterback Paul Justin by St. Louis, sixth-year running backs Travis Jervey and Rodney Thomas by Atlanta, safety Pat Tillman by Arizona, and John Avery, who led the XFL in rushing, by Dallas.

--Veteran NFL defensive tackle Eric Swann has retired because of chronic knee problems that sidetracked his career.

BOXING: Former boxing champion Pernell Whitaker said a mixture of medication and alcohol caused a seizure that sent him to the hospital Sunday afternoon, two days after his first fight in more than two years.

--Dave Hilton Jr., convicted in March of sexually assaulting two young sisters, was stripped of his WBC super middleweight title.

- Daily News Wire Services