If you’re a tennis fan, you probably want to see Serena Williams play at the U.S. Open this year. But for the good of the sport, you shouldn’t root for her to receive a wild card.

For Williams the younger, 2006 has been the worst of seasons. She began the year ranked just outside the top 10, and arrived at the Australian Open out of shape and seemingly out of spirit.After three rounds, Williams’ s title defense in Melbourne was over, and her season was put on hold, ostensibly because of a long-standing knee injury that did not heal properly, and also, she disclosed this month, because she needed a “mental break” from the game.

From January through July, Williams’ s ranking plummeted to no. 140, her lowest since 1997 (her first year on the tour). After her return to action last week, at the Western & Southern Financial Group Women’s Open in Cincinnati, her ranking stands at 108, and she may well need a gift from the United States Tennis Association come late August when the lights at Flushing begin to burn into the night.

A generous present indeed, and one that Williams would not deserve.

No, I’m not a Williams hater. I think she brings more energy to the court than any other woman on the tour, and I would prefer that she play at the Open and do well (frankly, I’d love to see her win it). But a player who admits that she needed a rest from the game should not receive a free pass into a Grand Slam tournament.

Williams is not the first champion to lose interest in tennis, and there’s nothing wrong with a mid-career nap. Bjorn Borg essentially walked away from the game after John McEnroe defeated him in the 1981 Wimbledon and U.S. Open finals (he was 25 years old). Mats Wilander reached no.1 in the world and then lost his ambition, and we all know the tale of Andre Agassi, who became well acquainted with the heights and depths of tennis over the course of a career that is winding down this summer.

In a sport that so taxes the mind and body for so many months a year, it would be astounding if a player of Williams’ s caliber did not have to walk away for a while. In Cincinnati, she said had “a lot of stuff” in her life that she did not care to describe — personal matters, one assumes — that kept her from training and tennis. There’s no need for Williams to explain further, but can we determine, from her comments and performance in Cincinnati, that her vacation is over?

Notice how you didn’t read anywhere that Williams returned to the court 10 pounds lighter, a few steps quicker, and with that long-lost zip on her first serve. She defeated one bad player, one average player, one overrated player (sorry, Anastasia Myskina), and then lost routinely to Vera Zvonareva, who is also making a comeback from injuries and a decline in the rankings (she is now at no. 37 after her victory over the weekend).

Here’s the difference between Williams and Zvonareva: the Russian went on to win the title in Cincinnati, and then she packed her bags and flew to California, Williams’ s home state, and took a wild card into this week’s Bank of the West Classic. Williams decided to rest until next week’s Acura Classic, and she has not yet asked for a wild card into next month’s Rogers Cup in Montreal, the most prestigious tournament leading up to the U.S. Open. A spokesman for the tournament, Louis-Antoine Paquin, said it was “highly unlikely” that the event would receive a request from Williams this late in the summer. And she is not among the confirmed entrants at the Pilot Pen in Connecticut the week before the U.S. Open, either.

In sum, Williams plans to play one more tournament before the U.S. Open. It’s hardly the schedule of a woman who has rekindled her love for the game, and certainly not deserving of a wild card.

For that honor, Williams should have to do some work. When Agassi’s ranking plummeted to 141 in the world in 1997 (a confluence of injuries and mental despair), he took a long, hard look at himse lf and decided that he could not fade away at age 27 and one major shy of a career Grand Slam. Agassi played two Challenger level tournaments that November in Las Vegas and Burbank, Calif., reaching the finals of one and winning the other. A year later he moved inside the top five; in 1999, he won the French Open (the only trophy missing from his mantel) and the U.S. Open, and returned to no. 1 in the world.Three more major titles followed.

I’m not faulting the USTA for saying it would offer Williams one of its eight wild cards into the women’s draw. As a business decision, inviting an icon like Williams is obviously the right choice. Only a moron would do otherwise. No, I’m asking Williams to turn down the USTA and follow the example of Agassi. She should prove that she wants to play tennis at the highest level again, rather than talking about it — unconvincingly — in a press conference.

If Williams needs ranking points and matches to sharpen her skills, she should be in Budapest, Hungary, this week, playing on red clay, and in Stockholm, Sweden, in two weeks, playing a Tier IV hard court event. And if necessary, she should compete for one of 16 qualifying spots to the U.S. Open the week before the tournament begins.

Imagine if Williams won the U.S. Open as a qualifier. That would be a fantastic story, and much better for the game as a whole.The sport deserves to have its top talents working as hard as they can and earning their keep, just as its lesser lights must do each day. Until Williams shows an interest in winning the hard way, I’d rather not see her get off easy.

tperrotta@nysun.com