Almost halfway through 2006, women’s tennis remains upsidedown.

So far this year, three different women have held the no. 1 ranking. Amelie Mauresmo, the current no.1,won her first major title in Australia after Justine Henin-Hardenne retired with what was officially scored as a “gastrointestinal illness.” Nadia Petrova, who dumped her coach in Australia because he was not “tough” enough, is now ranked no. 3 and has the most wins on the tour in 2006. Maria Sharapova is the second-best Russian, while Serena Williams, the most talented woman in the world, is the 14th-best American, ranked a lowly no. 108. And Martina Hingis has returned from a three-year retirement and moved quickly into the top 15.

How uncertain are things in women’s tennis? At this year’s French Open, which begins Sunday, the women have a rare opportunity. The eight major tournaments dating back to the French Open of 2004 have crowned eight different champions, including five first-time winners. The streak is the longest in the Open Era, which began in 1968, and one shy of the all-time record, last achieved in 1939 (see graphic).

It’s tempting to view this diversity among champions in an entirely positive light. The game certainly has more depth than it did in the days of more dominant champs like Martina Navratilova or Steffi Graf. More women slug the ball now than ever before, and more of them are supremely fit athletes, beyond being well versed in forehands and backhands.

Yet tennis remains a sport that demands a front-runner – a bona fide no. 1, if not a prodigy like Roger Federer – to give the rest of the pack someone to chase. Right now, no one seems quite ready to claim the top spot and dare a rival to steal it from her.

This perch should belong to Serena Williams. A case can be made that Williams is the most talented woman in the history of the game, and she is rapidly becoming its biggest waste of talent. Yes, she has long-standing knee injury that continues to nag her, but perhaps she would heal fully if she showed some interest in conditioning. This year, Williams has played three matches and fallen outside the top 100 for the first time since 1997, her first full year as a professional. She will miss the French Open and Wimbledon before a possible return later this summer.

So far this year, Petrova has enjoyed the strongest campaign. She lost to Sharapova for the fourth time in five tries in Australia, but since then she has won four titles, including her last three on clay. In Berlin, she defeated last year’s French Open champion, Henin-Hardenne, in three sets. She also defeated Mauresmo in a final in Doha.

Petrova’s defeats usually derive from mental errors or crises in confidence, not physical flaws. She stands 5-foot-10 and owns one of the most powerful, if at times inconsistent, serves on the tour. Her best performance at a Grand Slam came at the French Open in 2003, when she reached the semifinals.

There are no favorites in this tournament, but Petrova should be given better odds than anyone other than Henin-Hardenne, who’s still the best in the world on clay, and overall, if she is healthy.

For the rest of the field, the questions are numerous. Can Mauresmo withstand the pressure of being a top seed at her country’s home tournament? With a major title finally to her credit, Mauresmo has reason to relax. She doesn’t have many hours on clay this season, however, largely because she skipped the Internazionali d’Italia in Rome this month when she came down with a fever. In Berlin, she suffered a 6-1, 6-2 beating at the hands of Henin-Hardenne in the semifinals.

After winning her first Grand Slam title at the U.S. Open last fall, the oft-injured Kim Clijsters has played just 20 matches this year. In Rome, she struggled to beat the 70th ranked player in the world, then lost to an inconsistent Dinara Safina, the eventual runner-up.

Sharapova has one title this year, but has yet to play a match on clay, her worst surface. She missed Rome with a bruise on her ankle and may yet drop out of the French. Countrywoman Svetlana Kuznetsova continues to sprinkle mediocre performances with stellar ones, as does Elena Dementieva, a finalist at the French in 2004.

So little being certain, two players should have a fine chance to make this year’s French Open exciting: Venus Williams and Hingis. Neither player has won this tournament, and a victory would come as a welcome surprise. For Williams, clay does not suit her sometimes erratic strokes, though her speed and agility would be perfect for the surface if she played more like a scrambler and less like a slugger. Only Clijsters compares to her in terms of athleticism.

Hingis, who won her first tournament of the year in Rome, remains the story of the season. She has more craft than anyone on the tour other than Henin-Hardenne, and she seems to have settled comfortably into the role of underdog. If the more imposing women play their best, Hingis is a goner. Given room to operate, however, she might make the French Open the magical ninth major as the search for a leading lady continues.

tperrotta@nysun.com