Harold Solomon, the No. 6 seed and recent winner of the Western Tennis Championships in Cincinnati, outlasted 18-year-old John McEnroe. 7-6, 7-5, in a first-round match yesterday in the $125,000 Washington Star International tournament.

McEnroe, who gained fame three weeks ago when he reached the semi-finals of Wimbledon, gave Solomon all he wanted before a crowd of 5,400 at the Washington Tennis Stadium.

Solomon took the first set at 6-5, but Solomon broke him at 30 with a backhand cross-court winner, a bread-and-butter shot that had deserted him earlier in the match.

McEnroe took a 4-2 lead in the second set, but Solomon broke back at 15 as McEnroe played his sloppiest game of the match, and broke again at love in the 11th game. Solomon took control of the match after three deuces in the next game putting away a short lob with a decisively angled smash on his second match point, after McEnroe had two ads.

Guillermo Vilas and Rocoe Tanner, the lefthanders who are seeded No.1 and No.4 in the tournament, won their first-round matches yesterday.

Vilas, the powerful Argentinian who won here in 1975 after losing in the final to Solomon the previous year, played his usual strong backcourt game, hitting hard with topspin off both wings, to defeat Larry Gottfried, 6-2, 6-4.

Gottfried, 18, is the top-ranked junior in the U S and younger brother of Brian Gottfried, the No.2 seed in the tournament and the first man into the third tound Tuesday night.

Tanner showed impressively why he is called "the man with aces up his sleeve" as he bombed a dozen clean aces and numerous other service winners past Californian Dick Bohrnstedt in a 6-1, 6-4 victory.

New Zealander Brian Fairlie, the No.15 seed and semifinalist here last year, was upset by Terry Moor, the lefthander who beat Fred McNair IV of Chevy Chase in a first-rounder Tuesday night, 6-3, 7-5.

Dent's Australian Davis Cup teammate and doubles partner, 11th-seeded John Alexander, walloped Mike Cahill, 6-1, 6-4.

Aussie-born Bob Hewitt, who now plays Davis Cup for South Africa, won a long battle of groundstrokes in the mid-day sun from Colombian Alvaro Botancur, 2-6, 6-4, 6-4.

Hewitt, 37, bald and with a grayspeckled beard, looks a bit like Sean Connery in two of his recent roles: the elderly Robin Hood in "Robin and Marian" and Peachy in "The Mano Who Would Be King." He displayed both their savvy and youthful spirit in giving Betancur a lesson in tactics. Hewtitt may be old and slow, but his touch is unsurpassed.

No.16 seed Dick Crealy, yet another Australian, beat Tim Gullikson in the nail-biter of the afternoon on an outside court, 6-2, 3-6, 7-6. Crealy won the deciding tie breaker, 10 points to 8.

Ray Moore, unseeded although a semifinalist here last year, eliminated follow South African John Yuill, 6-7, 7-6, 6-2. Moore cruised after winning the second set tie breaker, 7-0.

Gottfried, who will be a sophomore at Trinity University in San Antonio, Tex. (his brother helped Trinity win the NCAA tennis title in 1972), looked exactly like what he is: a talented, promising junior getting a valuable but humbling lesson from one of the big boys.

He hit shots he thought were winners, especially off his formidable backhand, but Vilas got to them and hit offensive shots from what seemed like defensive positions. certainly young Gottfried never has seen as menacing a topspin backhand as Vilas', at least not from close range. "It was good experience for me. It's the first time I've played the top seed in a big tournament in front of a stadium crowd like this. I've seen Vilas on TV, and against my brother, but this was great for me," Gottfried said.

"I was nervous the first couple of games. I didn't know what to expect. I was trying not to be inlimidated by everything."

A point that spoke volumes came with Vilas serving at 3-2, 15-30 in the first set. This was Gottfried's best opportunity to get back into the set after listing his serve in the third game.

Eventually he hit a firehand cross-court long off a spirited rally of deep groundstrokes. Earlier he had lofted a good lob that clipped the sideline in Vilas' backhand corner. Vilas countered with a perfect defensive lob down the line.

Gottfried opted to keep the ball in play with a forehand instead of going for a moderately tricky overhead. After losing the point he looked as if he knew he should have been more ambitious. This was Vilas, not another junior.

Vilas appeared a bit sluggish but was pleased with his performance, given the potentially troublesome circumstances: sweltering heat and humidity; a heavy, rain-deadened court that got badly chopped up by churning feet: an opponent he was seeing for the first time, and the fact that he arrived only Monday from Kitsbuchel, Austria.

Tanner served nine clean aces in his first four service games, including four in one game. He also was coming in repeatedly on Bohrnstedt's backhand, and his approach shots were so deep and forcing that he got an extraordinary number of short lobs that he crunched away with overheads from the forecourt. At times Bohrnstedt must have felt that he needed armor more than a racket.

Tanner's serve is not the fastest on the pro tour, but it may be the best. His motion is quick and deceptive, the racket head coming through a low toss so quickly that it is difficult to read. He also mixes it up cleverly, hitting flat, slice and twist serves at a variety of speeds, to a variety of targets.

He served perhaps as well in the first set yesterday as anyone can on a clay court.

"I sure was hitting the corners well," he said with a satisfied grin. "I wasn't trying to serve that hard, but I wanted to move it around and get a rhythm. I wasn't going for aces, so maybe that's why I got them. The trick is placement more than raw power."

Tanner fell behind, 3-0, in the second set -- significantly, he was broken in the second game when he missed five of six first serves, his only bad service game of the match -- but then won five games in a row. Bohrnstedt held for 4-5, then Tanner served out the match, delivering his 12th ace on the first point and holding after one deuce.