Two of the 16 seeded players in men's singles, Raul Ramirez and Mark Cox, were eliminated and two others, Harold Solomon and Rosecoe Tanner, had narrow escapes today as the U.S. Open tennis championships began at the West Side Tennis Club.

Ramirez, whose confidence has evaporated with a string of bad looses this summer, was strangley docile and unimaginative in a 6-3, 6-2 loss to qualififer Ricardo Yoaza of Ecuador, 19, the junior champion here last year.

Ramirez, the Grand Prix champion in bothe singles and doubles last year, was seeded No. 6, a generous concession to past performance since he has lost to Brian Teacher (Washington Star International, first round), Greg Halder and Colin Dibley in recent weeks and has not reached the semifinals of any tournament since the French Open in May.

Cox, a 34-year-old Englishman who was seeded No. 13, was beaten, 7-6, 7-6, by 6-foot-4 Butch Walts, who had managed only two hours of practice outdoors on clay since playing the World Team tennis season with the Phoenix Racquets.

Cox, who appeared lethargic and distracted by the noise and hubbub around the grandstand court fought back from 2-5 in the second set, but lost the tie breaker, 7 points to 3. He lost the first set tie breaker by the same score.

Like Ramirez, COx's recent performances have not been the sort to inspire boldly confident shotmaking in the tight stages of a match.

He returned to North America and tournament competition after a four-week layoff at his new home in Epsom, where he had been tending to the dozen helter he is raising. He promptly lost in the first round of the Canadian Open (to Butch Seewagen) and the U.S. Pro Championships (to Ivan Molina) before coming here and tonight he was on his way back home.

Solomon, No. 12 seed from Silver Spring, Md., started shakily, used a one-hour rain delay to have his favorite racket restrung, pulled comfortably ahead in the final set and then nearly blew it before finally ousting Bernie Mitton, 3-6> 6-3, 7-5.

Tanner, seeded No. 11, broke NCAA champion Matt Michell when the Stanford junior served for the match in the second set. Tanner won the ensuing tie breaker, 7-3, and rolled to a 4-6, 7-6, 6-1 victory.

Nerves got to Mitchell. He had the match on his racket late in the afternoon, before what remained of the stadium crowd of 11,585. He double faulted as he served at 5-3 in the second set, and after Tanner whacked a beautiful back-hand down-the-line passing shot to make it 0-30, steered two back-hands long to lose his serve.

French Open champion Guillermo Vilas, the No. 4 seed extended his winning streak to 33 consecutive matches, and his clay court string to 40, with a 6-1, 6-0 victory over Manolo Santana. The smilling Spaniard, champion of 1965, is 39 and produces only glimpse of his old touch and brilliance in occasional tournament appearances.

For the first time in recent memory, there were three consecutive love sets on the stadium court as llie Nastase followed Vilas to center stage and annihilated Frew McMillan, 6-0, 6-0.

A bomb threat was phoned to the club by an unidentified caller who said that a bomb would go off in the stadium at 3 p.m. That was just before Nastate and McMillan went on court. New York City police made a search and found nothing suspicious. Spectators were not evacuated.

Bjorn Borg and Jimmy Connors, the No. 1 and 2 seeds, had their opening matches postponed one day so that they could rest, respectively, a wrenched shoulder and a strained back. They are scheduled to play first-found matches Thursday.

Ramirez, 24-years-old Mexican Davis Cup ace, is not injured, but he has a fractured psyche at the moment.

"I'm not playing to win. I don't know wxactly what it is. I'm hitting the ball well, I know I have the talent and the strokes, but I'm not thinking on the court," he said after his loss to Yeaza, who was coming off three weeks of hard practice under the supervision of former Australian Davis Cup captain Harry Hopman in Florida.

"I couldn't take advantage of important points. I couldn't turn the match around," continued Ramirez. "At 3-all in the first set, i said to myself, 'I'm going to break serve right here and that will be it." I played two good points to get up 15-30, and for the next three points, I didn't do anything.

"We played a long point from the baseline he hit two short balls, and I didn't go in. He won that point, the game, and he got ahead.

"For sme reason, I'm not bearing down on points like that. That's the best I can describe it. I didn't play deep, I didn't chip and go in, I didn't do anything."

Ycaza - whose 25-year-old sister, Anna Maria, is visiting him here, and predicted before the draw was made that he would play and beat Ramirez - served well hit most of the forcing shots in the match, played on an outside court.

A tall, pleasant youngster who an swers to the nickname "Flaco" ("skinny" in Spanish), Ycaza rallied patiently with Ramirez, seized his opportunities to get to the net, and saved himself with several lunging volleys off reasonably passing shot.

Solomon lost his serve in the first and last games of the first set, hurting himself by blowing four overhead smashes from inside the service line.

During practice in the morning, he thought that his favorite racket was too loose. He had it restrung, and then it was too tight. During the rain delay, which came after he broke Mitton in the opening game of the second set, he had it restrung again, and this time it came out the way he likes it.

As he served for the match at 5-3, 30-15, in the third set, Solomon double-faulted twice, then hit a lob wide. He wasted five match points on Mitton's serve in the next game - getting a bad line call on one of them - as Mitton held for 5-5 after six deuces.

"I was thinking a bit about last year," said Solomon, who lost in the first round here last year to Billy Martin. "I took the last two weeks off to get ready for this, and I thought I could be game again."

But Mitton's forehand, usually his strongest weapon, cracked in the 12th game. He made three errors off that side to lose his serve at 15, and Solomon was safely into round two.