As Gordon Bradley reached to open the motel door, he held his left hand back and against his chest. Five weeks ago, hurrying to cut his grass, the Washington Diplomats' coach put that hand inside a lawn mower.

"It looked like a grenade exploded in his hand," a doctor said. Bradley said, "I never thought I'd see it in one piece again."

All the parts are back in place. The thumb, index finger and middle finger are swollen still from the trauma of the terrifying accident and remarkable surgery. Total recovery may require several more operations over two years. Because the pooling of blood in the damaged hand causes intense pain, Bradley sleeps in a chair with the hand propped up.

But he is smiling today as his team prepares for Saturday's North American Soccer League match against the Tampa Bay Rowdies (WTTG-TV-5, 8 p.m.). "It's been five weeks now," he said, "and they tell me it is healing as if it had been five months."

Of Washington sports figures, none is more appealing than Gordon Bradley, 45, an Englishman who once mined coal five miles under the North Sea and played professional soccer 26 years, retiring only three seasons ago.

He speaks precisely, and his demeanor is courtly. He is the last guy you would expect to stick his hand in a lawn mower. Or the first, for there is about him a little-boy excitement that, as it sadly happened, would make him rush to cut the grass to get to a team practice early.

If the Diplomats ever make 50,000 customers rush to RFK Stadium, Bradley will have caused it. He would disagree. He would say Madison Square Garden, Inc., the team's owners, put up the big money to do it right. He would say the players did it. Fact is, the central intelligence in the creation of any sports team ultimately deserves credit or blame, be that intelligence the coach, the general manager or the owner.

George Allen was the Redskins' man. With the firing of a coach he hired, Max NcNab clearly became the man responsible for the Caps. For six years beginning in 1971, Bradley put together the Cosmos, hiring Pele and Beckenbauer. The Cosmos fired Bradley when he benched the owners' pet, Giorgio Chinaglia, and Bradley, no man's puppet, then came to work in Washington.

Bradley scouted, hired and coached most of the 27 Diplomats who began this season. This is his best team here, deeper at every position, more versatile offensively and more experienced defensively. With a 9-4 won-lost record nearing the midpoint of the 30 game NASL season, the Diplomats have the 1978 club-record 16 victories within reach.

But, like the coach himself, the Diplomats are feeling pain. Three key players are out with injuries: leading scorer Alan Green, No. 2 scorer and playmaker Joe Horvath and team captain Jim Steele.

"It is the same thing that happened to us last year," Bradley said. "We lost four players on a three-game road trip. Now I'm gone on another three-game road trip and three players are hurt. It is a sorry coincidence, indeed.

That three-game trip of 1978 destroyed a season's work. The Diplomats had won eight of their first 10 games, the best start in the franchise's five-year history. But after those injuries, the Diplomats lost all three road games - and the next three, too. From 8-2, the team wound up 16-14 and lost in the first round of the play-offs.

"We'll not do it this year," Bradley said. "I'm not saying we won't lose any more games, but we will not come apart the way we did last year. We have more depth."

As evidence of that new depth, Horvath's replacement Saturday will be Ken Mokgojoa, a first-teamer last year who set a club record by scoring goals in six straight games. The Diplomats put Mokgojoa on the bench by buying Horvath from the Rochester Lancers in February.

When Madison Square Garden bought the Diplomats last October, Garden President Sonny Werbin repeated his belief in the star system. The Diplomats, everyone assumed, would hit big stars over the head with rolls of thousand-dollar bills and become Washington's answer to the Cosmos, where every other player is a millionaire. The Diplomats would talk of Pele clones, not a Horvath and a Mokgojoa.

"That kind of thinking was premature," bradley said. "Everyone seemed to overlook the fact that Sonny Wermblin said the Diplomats would be a great team in three years."

Not that the Garden and Bradley didn't try big things immediately. They had an agreement with Kevin Keegan, an Englishman who is one of the best players in the world. But the deal broke down when a little-known rule - so little known, Bradley speculates, that it was cooked up specifically to spoil the Washington arrangement - was invoked to make Keegan stay in Europe if he wanted to play in that continent's most important championship. He chose to stay in Hamburg, Germany, where only last week the German players voted him the best in the league.

"Imagine how good he must be for Germans to vote an Englishman as the best player in their won league," Bradley said.

Bradley hasn't given up on signing Keegan. He keeps in touch by telephone, speaking to him even early this week. Though admitting Keegan is likely to play in Spain next year, Bradley said, "The idea of playing in America is beginning to appeal to him."

Bradley is less optimistic about getting another player he sought, Daniel Passarella, the team captain of Argentina's Wrold Cup champions. Passarella has signed a new contract with that team.

"Our chances of signing him are diminished," Bradley said.

"In a way I'm pleased that we're not rushing into signing these players," Bradley said. "I want our organization to be similar to the L.A. Dodgers or Dallas Cowboys. We want a good organization.

"There is always only one champion, and L.A. and Dallas don't win it every year. They still are good organizations that one would be glad to be associated with.

"If you achieve that, along the way you will win your share of championships."