It will probably not be the last Forest Hills, after all, but even if nostalgic farewells are delayed a year, there will be considerable activity worthy of note in this year's U.S. Open tennis championships, which begin here Wednesday.

It now appears doubtful that the proposed $6 million "racket park" that the U.S. Tennis Association (USTA) plans to build on the site of the 1964 World's Fair in nearby Flushing Meadow, will be completed in time for the 1978 Open. Therefore, USTA officials have quietly signed an option to stage the premier event of American tennis again next year at the West Side Tennis Club, where it has been played 60 times since 1915, and every year since 1924.

So it is not yet time to bid adieu to West Side's 16,000-seat stadium, built in 1923, where so much tennis history has unfolded beneath the stone eagles that perch atop the concrete horseshoe. Or to the gabled Tudor clubhouse, nestled in this relatively serene niche in the bustling borough of Queens, overlooking the grass courts still favored by club members even though the Open has been played since 1975 on a synthetic clay surface called Har-Tru.

The focus of this last and richest of the four legs of the traditional Grand Slam - total prize money (including Grand Prix bonus money) in the 10th Forest Hills of the open tennis era is a record $462,420 - will be on current events rather than reminiscence.

All eyes will be on transsexual Dr. Renee Richards, who got a court order to allow her to complete in her first major tournament since she became a woman; on Chris Evert, who is seeking to extend her 106-match clay court winning streak and capture her third straight U.S. Open titile, and on Wimbledon champion Bjorn Borg, defending champ Jimmy Connors and French Open titlist Guillermo Vilas, the protagonists in the scramble for the No. 1 world ranking.

There will be other fascinating centers of attention as 128 men and 96 women battle for the singles first prizes of $33,000.

The homecoming of flamboyant, ascending local players Vitas Gerulaitis and John McEnroe.

Gerulaitis, 23, won the italian Open on slow red clay in May and lost to Borg, 10-8, in the fifth set, in a Wimbledon semifinal that will be remembered as a classic of shot-making brilliance. McEnroe, 18, who was graduated from Trinity High in New York in June, is the juvenile sensation of tennis this year, the youngest semifinalist in Wimbledon's 100-year history.

The U.S. Open debut of Californian Tracy Austin, 14, the 5-foot, 90-pound prodigy who looked so impressive in losing to Evert at Wimbledon and recently won the national girls 18-and-under title.

The progress of Manuel Orantes, the popular 28-year-old Spanish left-hander who surprised Connors in the 1975 final here. He has recuperated rapidly since surgery in May to relieve a pinched nerve in his left elbow, annihilated Connors in the U.S. Clay Court final and was in his third final in four weeks tonight in Boston.

For the first time in one of the major international championships, the "point penalty system" will be in effect. Umpires will be empowered to dock players points or games for disruptive behavior in the most important experimental rules change since the tie breaker was implemented here in 1970.

Advance sales virtually assure record crowds for the 12 day and eight evening sessions, and CBS-TV will offer 26 1/2 hours of taped and live coverage, starting with 15-minute highlight shows the first three nights of the tournament (WTOP-TV-9 in Washington, 11:30-11:45 p.m.)

Evert is, naturally, the No. 1 seed in women's singles, but she has lost her aura of invincibility even though she has won 22 consecutive tournaments on clay.

But Evert was beaten in the semifinals at Wimbledon by Wade, and finished narrowly behind Martina Navratilova in the women's singles standings for World Team Tennis. She lost to Navratilova the two times they met in the second half of the WTT season, and was embarrassed by Wade, 6-0, as Wade's New York Apples crushed Evert's Phoenix Racquets for the WTT championship.

To defend her title, Evert will likely have to beat Billie Jean King, who has been working feverishly in a New York gym to regain her former strength after knee surgery last November, in the quarterfinals, and either Wade or Navratilova in the final.

If the seedings hold true, the quarterfinal pairings, in draw order, would be: Evert (1) vs. King (7), Sue Barker (4) vs. Wimbledon runner-up Betty Stove (5), Wade (3) vs. Rosemary Casals (6), and Navratilova (2), vs. Dianna Fromholtz (8).

Wade, who has celebrated her 32d birthday since winning Wimbledon, opens against Richards, who last played in the singles at Forest Hills in 1960 as Richard Raskind, in a match that is sure to receive worldwide scrutiny.

Borg, 21, who has already won two Wimbledon, two French, one WCT, one Italian, and three U.S. Pro titles, is seeded No. 1 in men's singles, and says this is now the title he most wants to win. He was runner-up to Connors in a magnificent final last year, 6-4, 3-6, 7-6, 6-4.

If the seedings hold up, the men's fourth round would look like this: Borg (1) vs. Dick Stockton (10), Gerulaitis (8) vs. Harold Solomon of Silver Spring. Md. (12), Vilas (4) vs. Ken Rosewall (14), Raul Ramirez (6) vs. Stan Smith (16), Ilie Nastase (7) vs. Mark Cox (13), Brian Gottfried (3) vs. Wojtek Fibak (15), Eddie Dibbs (9) vs. Orantes (15), and Connors (2) vs. Roscoe Tanner (11).

To win, Borg will likely have to beat Gerulaitis r Solomon in the quarters, Vilas in the semis, and Connors, Orantes, Dibbs, Nastate or Gottfried in the final. Borg is concerned about returning to clay after weeks on the fast synthetic court used in WTT, but he has been practicing hard with Gerulaitis.

Connors, who apparently is not concerned about the back strain that caused him to pull out of the U.S. Pro Tournament last weekend, has also been practicing in New York.

Vilas, meanwhile, has won 32 consecutive matches and six tournaments since Wimblelon, including five Grand Prix events back to back. He has a 39-match-clay court streak going back to the French, his first title of the big four.