Anyone who had forecast that even a lovesick Chris Evert would win a grand total of nine games in four sets against Tracy Austin and Dianne Fromholtz, and would be out of the $275,000 Avon Championships before the semifinals, surely would have been accused of jumping the gun on April Fool's Day.

But no, this is no joke. It happened, right before our disbelieving eyes. The Ice Maiden turned to slush. Her glacial composure melted. The Unsinkable Molly Brown of tennis players looked more vulnerable-and yes, more human-than we had ever seen her.

Christine Marie Evert-who until this year had not lost two matches in a row since she was a pony-tailed junior of 17-was beaten on successive nights by 16-year old schoolgirl Austin 6-3, 6-1, and Australian left-hander Fromholtz, 6-2, 6-3.*tAnd when the double-elimination portion of the eight-woman Avon playoff was finished, Evert was on the outside looking in at today's semifinals at Madison Square Garden.

A bit of history will put this startling development into perspective. This was the fourth time in seven tournaments she has played this year that Evert has failed to reach the semifinals. In the previous six years, she had been eliminated before the semis only three times in 110 tournatments.

All this leaves us to ponder whether we have witnessed a temporary shift in the balance of power in women's tennis-reversible when Evert gets over her preoccupation with her upcoming marriage to English Davis Cupper John Lloyd, and refocuses her mind on tennis-or a landmark event. Years from now, will we look back on this first Avon Circuit finale as the week the Chrissie era ended?

After her April 24 wedding, Evert, 24, undoubtedly will come out of the strange funk that possessed her this winter. She is a sensitive, family-oriented young woman, and it is hardly surprising that her imminent nuptials have monopolized her attention, at the expense of her tennis.

But it also is reasonable to surmise that she will never again be as single-minded in her pursuit of excellence on the court as she has been in the past. Circumstances, personal and historical, suggest that Chrissie will not dominate women's tennis a gain to the extent that she has the past five years. Perhaps no one ever will again.

"It may be impossible, because there's so much more depth in women's tennis today," said Austin, the heir apparent, after her first victory over Queen Chrissie Tursday evening.

"Up until a couple of years ago, it was very rare for any of the top eight women to be upset before the quarter-finals. Now it's different. There's more pressure in the early rounds every week. There are more good young players. It's tougher to be consistent."

Indeed, more amazing than Evert's collection of titles-two Wimbledons, two french, four consecutive U.S. Opens, four Virginia Slims Champion-ships, two Colgate Series Champion-ships-has been her awesome consistency, in matches and throughout seasons.

Consider this: since turning pro at age 18, before the 1973 season, Evert has won 76 of the 117 tournaments she has played, 503 of 545 matches.

In Wightman and Federation Cup competition, under the emotional burden of representing her country, she is undefeated in 23 matches.

She has not lost a match on clay, the surface on which she developed her oppressive back-court game, since August 1973. Her incredible clay-court streak covers 24 consecutive tournaments and 118 matches.

She took over the No. 1 world ranking in 1974, with a 103-7 record. In 1975, she was 94-6; in 1976, 75-5; in 1977, 7014; and last year, after a four month vacation at the start of the season, 56-3, undefeated after Martina Navratilova beat her in the Wimbledon final in July.

But in the first three months of 1979. Evert's record is 23-6. She has lost twice to Navratilova and once each to Greer Stevens, Sue Barker, Austin and Fromholtz-all in straight sets.

Suddenly, we have come to realize just how important willpower, her incomparable psychological domination of an opponent is to Evert's game. Without 100 percent concentration, she is mortal, even vulnerable.

The importance of "mental toughness" is almost a cliche in tennis, but with Evert, it is a palpable thing. Sitting in the stands-to say nothing of staring at her unflappable poker face across the net-one could always feel the intensity she exertd the power of concentration with which she energized every rally.

That singular psychic energy has been missing recently. Its absence was evident Thursday night, long before the tally of unforced errors she made against Austin reached 52-more than she has committed in a month at other times in her career. It was apparent in her listless form, her lact of fight and fire, against Fromholtz.

"I'm worried about her state of mind. She was just disconsolate out there," said Steve Flink, an editor of World Tennis magazine and a long-time, passionate admirer of Evert. "As soon as she got down, her heart went right out of it. I've never seen her like that. Maybe after the wedding. . . ."

But maybe not. Lobe is a many splendored thing, and it may never permit Chrissie to make tennis the most important thing in her life anymore, as it was for so long.

Many people who know Chrissie well expect her to retire before too many more seasons, to settle down and raise a family and never play competitively again.

She has said many times that once she has children, she will not come back to the circuit, or become a part-timer like Evonne Goolagong and Margaret Court. Her perfectionist and competitive impulses are so strong that she could not stand to play "social tennis" or to stay in the pro game beyond the time that she could challenge for the No. 1 ranking.