If the Tampa Bay Rowdies beat the Cosmos this afternoon, nothing will have seemed more improbable.

The Cosmos have the best record in the 12 years of the North American Soccer League. They have scored more goals than any other team in league history. They have a record of 28-1 over two years at Giants Stadium, site of today's 4 p.m. soccer Bowl. "We're just going to play our game," Tampa Bay Coach Gordon Jago said.

It probably won't be enough.

The Cosmos, defending their 1977 NASL championship, enter this Soccer Bowl as heavy favorites to defeat the Rowdies and become the first team to win back-to-back NASL titles.

The Cosmos ran up a record of 24-6 during the regular season and, since an embarrassing 9-2 playoff loss to the Minnesota Kicks, have won their last three playoffs games by a combined score of 10-0.

The Rowdies, on the other hand, got to this game by the slimmest of margins. After losing their opening semifinal playoff game to the Fort Lauderdale Strikers, 3-2, the Rowdies won the second game, 3-1, and the shootout, 1-0, to advance to the Soccer Bowl.

The Rowdies won the Soccer Bowl in 1975, beating Portland, 2-0, in their first year in the league. They were led then by Rodney Marsh, who remains the star of the team today. He finished fourth among league scorers with 52 points and is the man Tampa Bay will look to for offense today.

The Cosmos do not have to depend on one man even though Giorgio Chinaglia, league scoring champion with a record setting 34 goals, 11 assists and 79 points, is in the lineup. They are deep up front, deep at midfield and deep on defense. Their only possible weakness is in goal.

The Cosmos are expected to start Jack Brand in goal today. Brand shut out the Portland Timbers, 1-0, 5-0, in the semifinals but most soccer people claim that Mary Poppins would have a good goals-against average playing for the Cosmos.

Unlike most sports where the best offense is a good defense, soccer is just the opposite: The best defense is a good offense. The teams that have beaten the Cosmos this season have done so by getting out front early and continuing to apply pressure offensively. Few teams have succeeded against the Cosmos with defensive strategies.

The Rowdies do have an excellent young goalkeeper in Winston DuBose but no goalie alone can beat the Cosmos.

With Steve Hunt -- playing his last game before returning to the English League -- Dennis Tueart and Chinaglia up front, Franz Bechenbauer at midfield and Carlos Alberto and Werner Roth anchoring the defense the Cosmos have enough talent to stock three clubs.

Playing in front of a rabid Cosmos' crowd of 77,000 the Rowdies only hope is to score first and continue to press the Cosmos offensively throughout the game. Otherwise they are likely to lose by a wide margin.

When NASL owners scheduled the Soccer Bowl for Giants Sstadium they did so on the presumption that the game would be a sellout (it is) and that the Cosmos would be playing.

What they did not bargain for is an apparent mismatch created by two factors -- the imbalance between the strong, deep National Conference and the weak, expansion-riddled American Conference. The Rowdies 18-12 record, second best in the ASC, would have been fifth best in the NSC.

The retirement of Pele was expected to weaken the Cosmos on the field and at the gate. Instead they have broken league records in both areas. But the rest of the league has lagged behind.

Washington was one of several cities where attendance dropped. None of the six expansion teams proved to be a smash and already one franchise shift has been approved, with more expected.

The cosmos have made it in the New York area, averaging close to 50,000 fans per home contest. But the same cannot be said in the league's other 23 cities. Commissioner Phil Woosnam pushed for major expansion -- six cities -- after the 1977 boom year. Many say it was too much, too fast.

"Soccer is growing but it still has a long way to go in this country," Washington General Manager John Carbray said. "We have to crawl before we walk."

Attendance in many cities bears Carbray out. If the Cosmos were not included in the league figures, attendance from last season would be down. And, even though "Americanization" is a subject of constant discussion, the few American players see much playing time.

Gary Etherington of the Cosmos, a graduate of Mount Vernon High School in Alexandria and the NASL rookie of the year was only a parttime player. The Dips have six Americans on their roster but only Roy Willner and goalkeeper Bob Stetler, saw any extensive playing time.

The league must add two things next year if attendance is to improve balance and Americans.