The Redskins signed former San Francisco guard Ernie Hughes yesterday and could well add another offensive lineman today to combat a recent rash of injuries.

Hughes, a 6-foot-3, 250-pound second-year man from Notre Dame, started much of his 1978 rookie season but missed all of last year with a strained knee. He was cut in camp this year bythe 49ers.

"Ernie is a guard but we needed help there because Gary Anderson (Washington's backup guard) is playing so much tackle now," Coach Jack Pardee said. "And tackles are hard to find. We are still looking out there for one."

Washington has lost tackle George Starke for Sunday's game at Oakland and tackle Terry Hermeling is questionable for that contest. During yesterday's practice, Fred Dean and Anderson were the starting tackles.

Pardee said he would probably decide today whether another lineman is needed. If so, Starke will be placed on injured reserve. To make room for Hughes, tight end Phil DuBois, who has fractured ribs, was put in the injured reserve category and will be sidelined for at least four weeks.

"We want to wait a day and see how Terry responds to treatment," Pardee said. "If it doesn't look good for him, we'll have to make a move. And we want to see if George is going to be out three or four weeks or if he can come back quicker. If he can, we don't want to tie him up."

But Pardee didn't seem optimistic about Hermeling's chances of playing this week. "We'll see how he is later in the week but we are listing him as questionable just because that is what he is at this point."