The Washington Diplomats, slowly gaining the reputation as one of the stingiest defenses in the North American Soccer League, today hope to halt the Dallas Tornado's Brazilian Connection when the teams meet at RFK Stadium at 2:30 p.m.

The game will mark the U.S. head-coaching debut of Joe Mallett, Dip assistant coach who is handling the team in the absence of Gordon Bradley. Bradley injured his hand in a lawn-mower accident last week and is recuperating at George Washington Hospital.

"It's my first head-coaching job in America," Mallett said. "But I don't anticipat any problems. I've been in soccer more than 40 years now.

"We went about practice last week the same as if Gordon was right here. The players don't need any pep talks to get their adrenaline going.They want to win the game for Gordon Bradley."

Washington, 4-2 with 36 points, will have to pay close attention to the Tornado scoring trio of Zequinha, Milton and Jairo, all signed from Brazil during the off-season. The quick, flashy trio accounted for only four goals in six games, but are considered to be extremely explosive.

Dallas, 3-3, has been off to a slow start. The team has had injury problems and is just now getting healthy. Goalkeeper Alex Stepney, one of the top netmen in England for many years, anchors the Tornado defense which has yielded 92 shots and seven goals.

"I don't know much about Dallas except the three front men are quick" Mallett said. "We have to be alert. But the way we've been playing lately, we shouldn't have any problem with them."

The Washington defense has been outstanding. Last week in a 2-0 win over Tulsa, Washington allowed only four shots in the game. Dips' goalie Bill Irwin has allowed only five goals for an 0.80 goals-against average to rank second in the league. Irwin has been forced to make 21 saves, one last week against the Roughnecks.

"No, I haven't had a lot to do yet. That's because the people up front haven't allowed any shots," Irwin said.

The people up front ar e Tommy O'Hara, selected as NASL defensive player of the week for his part in the holding the Roughnecks to four shots, Mike Dillon, Don Droege and Robert Iarusci.

Not to be overshadowed, the Washington offense also has done its part over its six games. The Dips have out-shot their opponents by a 130-67 margin.