Washington Diplomat goalkeeper Jim Brown, instrumental in the team's early-season success, will miss Saturday night's game here against the Tampa Bay Rowdies because of a severely sprained ankle he injured in practice Thursday.

Dale Baxter, the 19-year-old back-up goalkeeper who has not played a game in the North American Soccer League, will start in goal for the Diplomats in the 7:30 game (WTTG-TV-5) at Tampa Stadium.

Brown jammed his left foot in a divot while running a wind spirit drill Thursday afternoon on the Diplomats' practice field outside RFK Stadium. He limped off the field and was examined by team trainer John Lally before being taken to team physician Stephen Haas' office in Chevy Chase.

An X-ray of Brown's injured ankle showed there was no break or ligament damage. The ankle "swelled up like a balloon late Thursday night," according to Dips' General Manager Duncan Hill.

"I spent 5 1/2 hours (in the Sports Medicine Center in Chevy Chase) taking ice treatment and whirlpool therapy," Brown said in a telephone conservation this evening."I'm going back tomorrow for awhile, too. I've had sprained ankles before, but nothing like this.

"There's a lot of pain at times," Brown continued. "I couldnht even get my boot on. But there's no reason I can't be back at practice by Thursday if I stay off it and do what the doctor says."

"You can't do anything about a severe sprain except wait," Lally said today in Tampa. Normally, it takes about seven or so days to recover. But that depends on the individual and how much the swelling goes down."

Lally said it was difficult to determine the extent of Brown's injury when the goalie first fell. If Brown had made a quick recovery, he would have joined the team Saturday morning. But Dr. Haas told Brown he would only aggravate the ankle by making the trip and that resting it totally this weekend would increase his chances of playing the Dips' next game -- May 17 against Dallas at RFK.

Brown has played every minute of the team's last 39 games, including seven this season. One of the top goal-keepers in the league, he played brilliantly in Washington's 1-0 loss to the Cosmos last Sunday.

Brown has allowed only eight goals in seven games this season for a goals-against-average of 1.14. The 27-year-old Scot had a finger broken in six places during the last indoor season, when a shot pinned his hand against the goal.

His style is reckless and he has taken several kicks, elbows and knocks this season, but never has left a game. Brown became the first goal-keeper in NASL history to score a goal when he tallied one last month against Atlanta.

Coach Ken Furphy, who did not attend a light team workout this afternoon at Tampa Stadium, could not be reached for comment.

Ironically, Tampa Bay played the Diplomats last week without its regular goalkeeper, Winston DuBose, who broke his hand the previous week. Kevin Keelan, whom the Dips tried to sign before the season, started in goal and the Dips peppered him with shots and coasted to a 4-1 victory in RFK.

Furphy had hoped to work Baxter in gradually, but he will start in place of Brown. If Baxter is injured, his backup is striker Paul Cannell.

The last time Baxter started a nonexhibition game was last July when his Canadian youth team played Mexico in RFK.

"I was wondering if I would ever get a chance to show the team what I can do," said Baxter, who is from Toronto. "Jimmy's played every minute of every game so I knew there was a possibility I wouldn't get that chance.

"It dawned on me I might start when I saw him go down," Baxter continued. "I've seen Jimmy get hurt before, but he always bounced right back. But this time, I could see the pain on his face and he couldn't put any weight on his left leg. I don't like that my first start may come under these circumstances. But it's a big chance for me to show what I'm capable of. I'll be nervous, but I'll just have to get over it.