"I think I can play at least half a game tomorrow, which is important for me," Beckham, 32, told reporters on Tuesday after taking part in his first training session with the Galaxy at the Home Depot Center.
"It's important for the team that I at least get on the pitch and help contribute. It was good to get out on to the field today and have a bit of practice.
"This is my first time, since I arrived, to be out on the training pitch and it felt good."
Beckham said he was still feeling some pain in his Achilles' tendon and under the ankle. "My ankle's not perfect," he added. "It's about 70-80 percent."
Galaxy head coach Frank Yallop said: "David is available to start and play a significant role tomorrow against D.C. United.
"I fully expect to give him his SuperLiga debut at some point in the contest. Tomorrow's game is very important to the club and we have a number of players injured or suspended so to have David available will be a big boost."
TACTICAL DECIDION
Yallop will have to decide tactically whether he prefers to start with Beckham, who is well short of his usual fitness level, or bring his high-profile signing on to the pitch late in the match to pile extra pressure on United.
"It's been frustrating for all of us not to have someone like David available," Yallop added. "I think David will be the one who knits it all together."
Beckham, one of the world's most marketable sports figures, has made only two fleeting appearances for the Galaxy since joining the Major League Soccer (MLS) club midway through last month.
He played for 16 minutes as a late substitute against FA Cup holders Chelsea on July 21 before making his MLS debut on Thursday at D.C. United, playing the final 21 minutes in a 1-0 loss before a capacity crowd of 46,686.
Signed from Real Madrid on a $32.5 million five-year deal, Beckham spent most of his first three weeks in Los Angeles receiving ice treatment and massage in the treatment room or working in the gym.
The former England captain twisted his ankle playing for his country against Estonia in a Euro 2008 qualifying match in June.
He then aggravated it in his final appearance for Real 11 days later when his former team clinched the Spanish league title.
