The Washington Bullets' problems continued to mount today when they were forced to put Dave Batton on the injured list because of a severely sprained right ankle.

To take Batton's place on the roster, the Bullets signed 6-foot-11 free agent forward-center Joe Cooper, who was cut by the Los Angeles Lakers during the preseason. Cooper, who was at his home in Houston, joined the Bullets in time for an evening practice today as they prepared to meet the Lakers Friday night at the Forum (WDCA-TV-20 at 10:30).

Batton was injured in the Bullets' 114-112 loss to the San Antonio Spurs Wednesday at Capital Centre. X-rays taken this morning showed no fractures, but Batton is expected to be sidelined at least a week to 10 days. So the Bullets placed him on the injured list. He must remain there for a minimum of five games.

Batton is the second power forward-center the Bullets have lost in the last four days. Spencer Haywood was placed on the injured list Tuesday with a strained calf. Carlos Terry, primarily a small forward-guard, was signed and that moved rookie Batton up to the top reserve spot for both Jeff Ruland and Rick Mahorn.

Ruland and Mahorn are prone to fouling; both fouled out Wednesday. Greg Ballard had to play power forward and, after Batton got injured, rookie forward Steve Lingenfelter had to fill in at center. "We just can't afford to get caught in a spot like that again," said Coach Gene Shue. "We needed some help right now."

Cooper, who attended the University of Colorado, was a fifth-round draft choice of the New Jersey Nets in 1981. After being released in the preseason, he spent last year playing for Lancaster in the Continental Basketball Association. The Lakers signed him as a free agent.

"He played well for them," said Bullets Assistant Coach Bernie Bickerstaff, "but when (Bob) McAdoo finally signed a new contract, they didn't have any room for him."

Wednesday's loss to the Spurs was the Bullets' fourth in a row and fifth in their last six games, not the best of circumstances with which to begin a four-game road trip.

After Friday's game with the Lakers, the Bullets play the San Diego Clippers Saturday night, the Phoenix Suns Wednesday and the Indiana Pacers next Friday before returning to Capital Centre to play the Portland Trail Blazers a week from Saturday.

The Lakers have been struggling lately, too, having lost two straight, including a 118-117 setback to the Mavericks in Dallas Wednesday when Mark Aguirre made two three-point shots in the final 17 seconds, the last one with one second remaining.

Shue made one change in his lineup against the Spurs, starting Billy Ray Bates at shooting guard in place of rookie Bryan Warrick. Bates scored 14 points and his backup, Don Collins, made seven of eight shots and also had 14 points. Warrick didn't play.

The team's biggest problem right now is poor free throw shooting, Shue said. The Bullets missed 13 of 31 against the Spurs, 11 of 23 against New York and 11 of 25 against Detroit in three of their last four games.