Vitas Gerulaitis played and won the Italian Open Tennis Championships last year, all the while accumulating sizable fines for being truant from the Indiana Loves of World Team Tennis. He competed in Rome not only because he enjoys La Dolce Vita, but because it was a condition of his contract with clothier Sergio Tacchini.

Cino Marchese, the public relations director of a competing manufacturer, La Font, is a patriotic Italian. But when Australian Phil Dent played hometown boy Antonio Zugarelli in the semifinals here last year, Marchese sat in the stands at Foro Italico and cheered madly for the lad from Down Under.

"I am a very good friend of Tonino, I know him since he was a boy, but Dent is wearing my clothes and I need him in the final, for the television exposure," explained Marchese. "I cheer from the wallet, not the heart."

Giodano Maioli, a former international player who now represents Australian, yet another of the numerous Italian tennis haberdashers, was married last Saturday, but the occasion was not as joyous as it might have been.

"Eddie Dibbs ruined my wedding day. I was so depressed," he said after Dibbs lost to Bjorn Borg in the Italian semifinals in less than two hours. Dibbs is the highest-ranked player contracted to wear the Australian line, and Maioli expected him to keep the Italian-made kangaroo logo in front of the TV cameras somewhat longer.

These are just a few manifestations of what could be called The Great Italian Tennis Clothes War, a battle of companies as fiercely competitive as the players they outfit and pay to endorse their apparel.

At stake are shares of the tennis-wear market in Italy, where sales are estimated at between $50 and $70 million annually. In the rest of Europe, the Far East and Australia, where the volume is at least twice as great, and in America, which Marchese calls, with an appropriate flourish, "The golden land, where the market has no limit, and you can do impossible things if you have the right idea."

The body-fitting Italian look is "in" for tennis clothing, and no less than 50 Italian companies of various sizes are trying to exploit it. The largest are Fila, Tacchini, Australian, La Font, Ellesse, General Sport (half owned by Italian tennis star Adriano Panatta) and Maggia (the Italian version of Interwoven's, "John Newcombe Moustache" line).

Tacchini was the first to market in the United States, three years ago, but in the past nine months Fila has sold more than $3 million worth of goods in America, taking the lead.

The distinctive Fila styles, widely exposed on TV by Borg and Guillermo Vilas, have been well displayed in leading specialty stores and tennis boutiques, and only limitations in production capability have kept sales from skyrocketing.

"Italy is famous for its clothing, and has been able to put the Italian styling into tennis wear," says Marty Mulligan, a top Australian player of the '60s who has lived in Italy since 1964 and now, as Martino Mulligano, represents Fila in tennis.

"The Fila family was very big in ski clothes and other sportwear, and they arrived on the tennis scene at the same time as colored clothing, which was very important," says Mulligan, "If people have nice figures, they like to show them off - especially women - and the American styles are not as figure-flattering as the Italian."

A Fila or Tacchini shirt that retails for $25 in Italy sells for $40 at Neiman-Marcus. A track suit that costs $70 in Rome is $110 or more in U.S. stores, largely because of an import duty of 35 percent on cotton-embroidered goods and 42 percent on embroidered polyester garments.

Nevertheless, Americans buy the Italian clothing almost as fast as the manufacturers can supply it. This is why La Font has recently opened a U.S. headquarters in Newport Beach, Calif. (If you capture California, you have captured the United States). Australian has signed the American Dibbs, and Ellesse and General Sport are longingly eyeing the American market.

"Everywhere else, we know the amount that it is possible to sell, but the U.S. is so big we do not know," says La Font's Marchese.They say there will be 50 million people playing tennis in the U.S. by 1985. Even if most of them wear T-shirts and cut-off jeans, if we can get only 5 percent of the market, we can make a fortune.

"These are rich people. They are happy to pay $40 for a shirt that is not that much better quality than a $10 American shirt because they are crazy for the Italian look."

While the tennis boom in Europe is still in its early stages, the sport's percentage rate of growth is almost as phenomenal as it was in the U.S. in the early years of the decade. The Italian manufacturers see America as their future.

"Italy has the Red Brigades, Germany has other social problems, England is too old, France too snobby, Spain is still sleeping like a baby," says Marchese. "In Africa, the future is for the blacks. In South America, you wake up in the morning and they have given the government to somebody else. The Far East is a big question mark. But in America, you can plan your business five years ahead and know the government and the money will be there."

While all the Italian companies are tiny compared to the German-based Adidas and the major American manufacturers, they have been major factors in the bidding for professional players to wear and endorse their attire.

Fila pays both Borg and Vilas well in excess of $100,000 for their personalized lines, and also has contracts with Harold Solomon, Dick Stockton, Evonne Goolagong, Kerry Reid and a number of European men and women.

Tacchini has more than 45 players under contract, paying hefty sums to such heavyweights as Gerulaitis, Brian Gottfried and Roscoe Tanner, and modest amounts to lesser players.

Any international player can get free clothing from any of the companies if he or she is willing to wear it without being paid to do so.

"When I started my company 10 years ago, I thought the players helping us in our marketing should be paid. I was the first to have contracts with the players, which I think is proper and correct, says Tacchini, a handsome former Davis Cup player for Italy.

"I still have a tennis-player mentality. I have a strong spirit of friendship-among-sportsmen with the players I have under contract. It is not like a relationship between employer and employe - we have a different ambiance, like a team."

A player in the Top 100 in the computer rankings of the Association of Tennis Professionals (ATP) can expect at least $5,000 per year on a clothing contract - more if the player is ranked high in a specific market, such as a European country, according to Richard Evans, former European director of the ATP and now a tennis consultant in London.

Players in the Top 50 can expect $8,000 or more, those in the Top 35, $10,000 and up, those in the Top 10, $15,000 and up.

The game's major personalities - Borg, Vilas, Ilie Nastase, Jimmy Connors, John Newcombe, Arthur Ashe, Rod Laver - can almost write their own tickets, commanding as much as $200,000 per year, including royalties on their "autograph" lines.

"For the right personality, there is no limit - especially if he is willing to sign a long-term contract and do promotion, such as Newcombe (Interwoven), Nastase (Adidas) and Ashe (Catalina) have done," says Marchese.

"Personality is very important. We are about to sign a contract with the Gullikson Twins. Tim and Tom. It is possible to do some very nice advertising and promotion with twins, especially in the United States."

Marchese - a tall, genial, gray-haired former basketball player who is nicknamed The Silver Fox - signed three Australian players to launch La Font's tennis line in 1976: John Alexander, signed for a reported $18,000 per year, was the focal point of advertising and poster campaigns. Countrymen Phil Dent and Kim Warwick received lesser contracts.

Marchese looked liked a genius when Alexander came to Rome with the Australian Davis Cup team, beat Tony Roche out of a singles berth, and then defeated the top two Italians, Panatta and Corrado Barazzutti (Ellesse), in the televised 1976 semifinal won by Italy.

Last year Dent reached the semis of both the Italian and French championships, and Alexander beat Panatta in a five-set classic to clinch the Davis Cup at Sydney, the climax of 17 hours of the Australia-Italy finals on television in both countries. Whe La Font clothing was introduced in Australia this year. $1 million worth was sold in 15 days, Marchese says.

Now Marchese is looking for a concept to captivate the American market. "America is very celebrity-conscious. I thought maybe we should concentrate on Chad Everett, Alan King, Farrah Fawcett, all those stars who play tennis." he said, "but it is very difficult to explain to your boss, who has never been to America, who Farrah Fawcett is.

"In America, if you have the right idea, it is possible to do anything. If you can give your product a feeling of the good life, you can have very big success. I think Tacchini is very smart to sign Gerulaitis, because the people see Vitas driving a white Rolls-Royce, dancing at Studio 54. escorting a beautiful lady on each arm and wearing Tacchini tennis clothes. This is the kind of life they want.

"I have an idea for America, how to associate La Font with great charisma, but I don't tell you what it is," Marchese adds with an irresistible smile."If it works, I will be very rich, and I won't need Borg, Connors, Vilas or anybody to help sell my clothings."

Meanwhile, the auction for player endorsements and the battle of marketing strategies continues, even though no one can estimate just how much impact a pro wearing one manufacturer's clothes has on sales.

"It has become very competitive," sighs Tacchini, who speaks of his garments lovingly, stressing the craftsmanship and the expensive Egyptian cotton. "It is like when a fisherman says, 'Over there are big fish,' and suddenly there are so many fishermen that you cannot move in the water."