Guillermo Vilas will not win the U.S. Open this year. He is not playing anywhere near his peak and 1979 probably will end up as a lost year for him.

These are not Vilas' critics talking. "it is his coach and best friend, Ian Tiriac, talking. The man, who many in tennis feel "made" Vilas, now believes he has a rebuilding job to do.

"He's lost some of the confidence he had in '77," Tiriac saidm dragging on a cigarette moments after he and Vilas had won a doubles match Thursday night. "He's done too much switching of surfaces, played too much indoors. He doesn't feel as confident on clay as he once did.

"Right now this is a sacrifice year. If h can win two or three tournaments, that will be fine. But we are not expecting too much. He needs to work."

Work is Tiriac's buzz word. When the fiery Romanian became Vilas' coach in 1975, the young Argentinian was known as one of tennis' top talents, a top talent who could not win big matches.

According to Vilas, Tiriac changed all that. Under his tutelage, Vilas won the French and U.S. opens in 1977, was player of the year that same year and won the Australian Open in 1978.

But 1979 has not been the same, Vilas has dropped to No. 6 in the ATP computer rankings. He lost the Italian Open final to Vitas Gerulaitis after leading, two sets to one. He was beaten in the second round at Wimbledon and in the first round at Gstaad in Switzerland.

In Washington, he has not yet faced a tough challenge although he insists that he is pleased with his game. "I am hitting the ball better now," he said. "The problem has been confidence and concentration. I am getting them back now. My game is getting better."

Tiriac is not so sure about the concentration. He wishes that Vilas would think about tennis more and poetry and music less.

"He is still very interested in things outside of tennis, unfortunately," Tiriac said. "I wish he would think only about tennis because that is the only way to succeed in this game today.

"You cannot be concentrating on other things when every day you are playing people who only drink milk and play tennis. That is the way it is today."

Tiriac speaks very fast, leaning forward to make his point, his huge head shaking back and forth. With his large busy mustache, his black hair and his never-changing impassive stare, Tiriac has frequently been called the most sinister-looking man in sports.

That reputation dates back to his days on the Romanian ice hockey team in the early '60s. It grew in the early '70s when he and Ilie Nastase played Davis Cup together for Romanian and frequently got into shouting matches with umpires, opponents, spectators and each other.

Now, known in tennis circles as Vilas' "guru," Tiriac says he doesn't care what people think about him. "I stopped worrying about what people said or wrote when I was playing hockey," he said. "I understand what reporters are trying to do and I try to cooperate But I don't care what they say. I don't read the papers. Neither does Villas."

Tiriac, who says he is 40 although some claim he is 45, already is planning a comeback for Vilas next year.

"We will play the U.S. Open and then we will start working for next year," he said. "I don't see how he can win in Flushing (new site of the Open) because the courts there are designed for keeping foreign players from winning. They put in the hard courts to try and make more Americans win."

Under Tiriac, Vilas, who will be 27 next month has proven himself to be more than a clay court player, winning the Australian on grass and the 1977 Grand Masters in Melbourne on grass. But he has lost his dominance on clay as a result, according to Tiriac.

"Once he was the absolute master on clay. I worked to make him more aggressive; that is why he can win on other surfaces now. But he has lost some of his steadiness.

"Next year there are some tournaments we will jump over so he can concentrate on working up to the French and the Italian in the spring."

There are many in the tennis world who cannot fathom the relationship between Vilas and Tiriac. Vilas is considered an intellectual, Tiriac single-minded and shrewed. Vilas brushed off the question simply: "What I am what I have accomplished, he has done. He has made me what I am.

Tiriac explains things differently. "We are completely opposite. The music he likes, I hate. The movies he likes I hate. The food he likes I dislike.

"We are friends but we are kept together by our working relationship. We are able to live together because we are able to work together. We try very hard to cooperate with each other."

Tiriac says when he stops coaching Vilas he will stop coaching.

And Vilas say Tiriac will be his coach as long as he plays the game. "He is part of my game," Vilas said. "Together we will win again. CAPTION: Picture, Ian Tiriac, the good coach, carries student, Guillermo Vilas, across quagmire after heavy rain at Star International Tennis Tourney. By Richard Darcy - The Washington Post