Saturday's preseason game between the St. Louis Cardinals and the Minnesota Vikings at Wembley Stadium is just the first step in what the National Football League hopes will be a five-year drive into the lucrative European television market.

The last NFL game sanctioned outside North America was in Tokyo in 1976, when the Cardinals beat the San Diego Chargers before a crowd of 27,000.

Now Japan is the NFL's largest overseas market for football films, television specials and merchandising.

With the astonishing success of last season's live screening of the Super Bowl, when an estimated 4 1/2 million people tuned in here and stayed put until 2:30 in the morning, this seems to be the time for the league to test Europe.

NFL Commissioner Pete Rozelle, whose presence in London shows how important this is, said he wants to see the reaction to Britain's first up-close look at the game.

"For 15 years the NFL and the State Department have been looking to bring football to Europe.

"We know we can't export it here," said Rozelle, "but we can play it here to develop interest.

"I'm hoping that within five years we might have a live game being televised in Europe each week by satellite."

Saturday's game is a sort of loss leader on which no one expects to come close to breaking even. The whole package has cost entrepreneur John Marshall, who put the deal together, $1 1/2 million.

He would have to sell all 68,000 places at Wembley to make that back but expects somewhere between 30,000 and 40,000 to turn up. The ticket prices range from $7.50 to $75.

Marshall, though, is prepared to accept the loss. "I've taken out a five-year option on Wembley and even if we lose $500,000 this year we are prepared to carry on," said Marshall. "If at the end of the game on Saturday we all want to see it again next year then that will count as a success."

The Cardinals and the Vikings wanted a neutral venue for their preseason game and volunteered to play here when the NFL asked.

It hasn't been easy. Although there have been minor headaches, like finding 400 towels and 850 pounds of crushed ice, the major problems have come from a lack of communication.

It took a bit of gentle persuasion to have the 30-second clocks moved back from the 50-yard line, where they had been installed, into the end zone. And however much the two countries like to think they speak the same language, that's hardly the case; for example, team buses here are called the team coaches, whereas in the United States, trainers are regarded as coaches.

The Wembley Stadium officials couldn't figure out why the teams wanted places for the coaches in the press box. But the English have a certain morbid fascination of all things American and those language difficulties just tend to get laughed off.

American football's success on television in Britain is no doubt attributable in part to that fascination, plus a sneaking admiration for the brashness of America. This has been a sporting nation, especially for the past 10 years as social patterns have changed and leisure facilities have multiplied.

Attendances for the major British sports of soccer, cricket and rugby have dropped and there is now room for sports like basketball, ice hockey, squash and even American football.

Television watchers look on the game as a melee of extra large men, padded up like astronauts, smashing into each other in a somewhat crazed effort to see who can cause the most damage. But there is a growing awareness among the game's aficionados and many have perhaps come to see that football is, in Rozelle's words, "a disciplined form of violence."

The game is being televised in 11 countries and will be shown live in St. Louis and Minneapolis. In a few hours we'll have our first indications whether soccer-mad Europe is ready for the razzmatazz world of American football.