There is no such thing as a crucial North American Soccer League game in April. But for the Washington Diplomats, Sunday's match here against the revamped Toronto Blizzard represents a change to take a major step forward in this still-young season.

The Diplomtas are 2-2, both victories at home, both losses on the road. They would love to pick up a road victory here to keep up the momentum of their two-game winning streak; to prove to themselves that they can win outside of RFK Stadium, and to show Toronto, a fellow member of the National Conference East, who is boss.

The Dips will be aided by the presence of Joe Horvath, who was expected to miss this game with a slight break in his left foot, in the starting lineup. The rambunctious Hungarian trained with the team in Exhibition Stadium this afternoon and Coach Gordon Bradely said Horvath, a key figure in both Washington victories, will start Sunday.

Horvath will be needed for Washington to win on Toronto's artificial turf. The Blizzard is 1-2 on the year, but under new President Clive Toye is a much different, much improved team compared to the club that was 14-16 a year ago but still good enough to beat Washington 2-0, here.

"They've got a good bit of talent and they have always been tough up here," said Bradley, who is 1-3 against Toronto as Washington's coach. "But I just have a feeling about this game, a good feeling. Don't ask me why I do. I'm not hearing complaints about the turf like in Tulsa. I think we'll be ready and do well."

The Dips come into the game with a number of nagging injuries: goalkeeper Bill Irwin has a pulled stomach muscle; Johan Cruyff is slightly bothered by a pulled leg muscle, and Sonny Agnew had a badly bruised foot. All are expected to play.

Toronto is healthy but Coach Keith Eddy said today he will make one major change in his lineup. benching defender Willie MCvie in favor of Italian international Francesco Morini, 35, who was acquired on loan during the offseason largely because Toye wants to appeal to the 400,000 Italians who live in Toronto.

Washington's major concern however, will be striker Ivan Lukacevic. The 6-foot-2-blonde Yugoslav has three goals against the Diplomats last season. all of them off of head shots.

I've never seen anyone get up in the air like him on a soccer feild," Washington defender Bob Iarusci said today. "He's so quick and so strong. He's as dangerous as any player in the league."

Last year Washington had no one on the back line who could match Lukacevic's size or strength. But now, with Nick Mivatovic in the lineup, Bradley feels better about the matchup. Mijatovic also is 6-2 and showed last week against Dallas that he is capable of dominating the defense zone from the air.

At the other end of the field, the Blizzard has improved considerably, especially in goal. When Toye moved from Chicago to Toronto last winter one of his first moves was to acquire Chicago goalkeeper Tony Chursky, a Canadian who is an outstanding NASL goalkeeper.

"He won't make mistakes," said Alan Green, Washington' leading scorer with four goals. "There won't be any gift goals. We'll have to work to score."

Chursky will be supported on defense by Morini, Peter Roe, Colin Franks and Jim McAlister, perhaps the most intriguing of Toye's off season acquisitions. In 1977, McAlister was the NASL rookie of the year in Seattle and was considered likely to become the league's first great American-born player.

Symbolically, after the Cosmos' 2-1 win over Seattle in the Soccer Bowl that year, Pele, playing his last NASL game, gave McAlister his jersey. Seemingly, a passing of the torch.

But it has not worked out that way. In fact McAlister was benched for much of the second half of Seattle's 1979 season. Now he is starting anew, and starting on defense, for Toronto.

Toronto also acquired South African Jomo Sono for cash, from Atlanta in the off-season. Sono is another young player (24) who has never lived up to his early potential. But he is starting here and is one of the leaders of an aggressive Toronto midfield.

"We have to hold their midfield back early," said Iarusci who played on Toronto's Soccer Bowl championship team in 1976. "At home, they'll try to take over. We can't let them do that. We have to start aggressive and stay aggressive. That is the only way you win on the road in this league."

Danny Molendyk, acquired by the Diplomats before the 1979 season, will return home to Holland Tuesday with permission from the team to make a deal for himself. Molendyk played one game last year and one game this year for Washington. Mike Zimet has been fired from the Diplomats' radio broadcast team after four games. "Mike just wasn't ready," General Manager Andy Dolich said. TV play-by-play man Mike Lange will work with Scotty Morrison on radio during road games while Art Welch, the former Diplomat, will join Morrison at home . . . Cruyff was in a playful mood when the team arrived in Toronto this morning. As the Diplomats' party was passing through customs he said to someone behind him, "Have you got the stuff," just loud enough for the customs man to hear. It took five minutes to convince the agent that even superstars kid around, too.