Their undefeated streak of one goes on the line tonight at 8:05 when the Washington Capitals play the Flyers in the home opener at Capital Centre. The teams play again in Philadelphia on Sunday night.

Washington began its season in New York Wednesday with a 5-4 victory over the Rangers. The Flyers beat the Nordiques, 9-5, a day later, scoring three goals within 35 seconds.

"They (Flyers) probably forecheck as well as any team in the league," said Capitals Coach Bryan Murray yesterday. "They did give up a lot of chances to Quebec, and their defense wasn't as mobile as it had been (during the preseason)."

Even so, Murray knows his club will get a full night's work against the Flyers. Amid the giddy optimism surrounding the Capitals' first victory, Murray remains realistic.

"I wasn't jumping for joy," he said. "It was only one game, and we've got to remember that. We indicated that by hard work, we will be a contending hockey team."

Yesterday, the contenders were honored at a Touchdown Club luncheon. "Our players wouldn't miss a free beer or a free lunch," deadpanned Rod Langway, newly named captain.

Loyalists who paid the $12.50 admission price were treated to up-close-and-personal glimpses of the Capitals. "Are the players coming? Where are they?" one woman kept asking after the Capitals had filed into the dining room.

With one player or less per table, the conversation ran mainly to autograph requests and gushy predictions for the rest of the season. Milan Novy, whose English vocabulary does not yet include cocktail-hour chatter, smiled, listened and ate.

Looking nifty in a navy velvet jacket, Langway was asked to say a few words, along with Murray, General Manager David Poile and owner Abe Pollin.

"We're gonna have fun this year," Langway said. "We'll try to work 60 minutes, but you do have lapses. This is a new challenge for myself, but if you don't enjoy what you're doing, get out of it. I plan to stay (with hockey) as long as I can . . . it's good money."

Pollin promised that "We will sell the place out and we will play great hockey." As of yesterday, there were still approximately 1,500 tickets remaining for the Flyers game.

Murray stuck with what those in political circles would call cautious optimism. "We're very optimistic, but we're very realistic as well."

Realistically, he said later, his team will take advantage of its strong point, speed. "We need at least six defensive contributors against Philadelphia because it will be more of a contact game (than with New York)," he said.

Calling it a "potentially good line," Murray said he would start the Mike Gartner-Novy-Bobby Carpenter unit against the Flyers. That trio accounted for eight points against the Rangers.

Assistant Coach Terry Murray, who scouted the Flyers' opener, said the bruising Philadelphia club has changed its tactics a bit. "They're concentrating on playing the game a little more," he said. "They still take the man out, and do the clutching and grabbing, but it's not the same."

During the offseason, the Flyers acquired defenseman Mark Howe and Miroslav Dvorak, a former Czech national team teammate of Novy. "Those guys are an indication that they're not the same kind of team," Terry Murray said. "It is physical, but it's a different type of game."

Scribbling a last autograph or two yesterday, Langway briefly looked ahead to Sunday's game in the Spectrum.

"I enjoy playing in Philadelphia," Langway said, twisting the Stanley Cup ring he got in Montreal. "I take my energy from the crowd. To hear them booing affects players, and we'll take it right from them."

Injured goalie Dave Parro skated with the team yesterday. "He's stopping pucks pretty well, and I suppose if I had to, I could play him Sunday," said Murray. "But (Pat) Riggin will start (Saturday) and I'm not ever sure who the backup will be." Soviets to Play Here

NEW YORK, Oct. 8--A Soviet all-star team, primarily made up of players from the world championship squad, will play a six-game "Super Series" against National Hockey League clubs Dec. 28 to Jan. 6, the NHL and the NHL Players' Association jointly announced today.

The Soviet team will open Dec. 28 in Edmonton against the Oilers and Wayne Gretzky, then travel to Quebec Dec. 30 for a game with the Nordiques and the Stastny brothers and will visit Montreal Dec. 31.

The Soviets play Jan. 2 in Calgary against the Flames, Jan. 4 in Minnesota against the North Stars and close Jan. 6 in Philadelphia against the Flyers.