When the spotlight comes up on Venus and Serena Williams at MCI Center Thursday night, Zina Garrison plans to be in the stands taking in the tennis exhibition on two levels: as an unabashed fan of the two most recognizable women in tennis, and as their occasional coach and mentor.

It's an evening billed as sheer entertainment, designed to give Washingtonians their first look at the Williams sisters in competition -- albeit a friendly competition, with no prize money, title or trophy at stake. As the sisters swap strokes during this final stop on their three-city "Williams Sisters Tour," Garrison, the U.S. Federation Cup captain, will be probing more deeply than most for evidence of the sisters' fitness, hunger and commitment to tennis with the 2006 season just weeks away.

Neither Williams sister has been seen in competition since September, citing injury and fatigue in bowing out of their final tournament commitments. Even before their premature exit, it was hard to sum up their games as 2005 drew to a close. The former world No. 1's were alternately brilliant -- with each winning another Grand Slam title -- and error-plagued.

Serena opened the year by winning the Australian Open but ended with her lowest ranking (11th) since 1998, admittedly out of shape.

"I don't think I did too well, but I can't tell you how many people would have dreamed to have had my year," Serena said in a telephone interview. "It just goes to show you I'm really just trying to be the best I can."

Venus had a dazzling resurgence at Wimbledon, where she toppled world No. 1 Lindsay Davenport in the longest women's final in tournament history and celebrated by jumping with uncontrollable glee. She immediately traveled to Russia for a Federation Cup match, but the strain took its toll. She finished the year ranked 10th in the world.

"The season is very long," said Venus, 25, who has been playing professionally since 14. "It's pretty challenging to have to play year after year, for 10 months a year, for a human -- not a machine. You just have to watch out for yourself."

With an eye toward better results in 2006, Venus says she has been working out diligently. Facing Serena in fan-friendly exhibitions in Seattle and Cleveland before Thursday's finale in Washington is also helping her prepare for 2006, she says.

The "Williams Sisters Tour" has a philanthropic component, as well, benefiting the Ronald McDonald House and, locally, Washington's Southeast Tennis and Learning Center. The Washington Post is among the event's sponsors.

"This is perfect for us because obviously we haven't played the last few weeks of the season," Venus said. "To be able to kind of test out ourselves and also to try new techniques just gets me really excited for next year. I'd like to be more aggressive on the court, but more than anything, I'd like to stay healthy next year."

Legions of the sisters' fans, however, are less concerned about whether they reclaim their place atop the sport in which they have a combined 12 Grand Slam titles (seven for Serena; five for Venus).

They regard them not simply as world-class athletes, but as role models, trendsetters and trailblazers. Venus made history in 2002 as the first African American, male or female, to rise to the No. 1 ranking in tennis. Later that year, the sisters became the first siblings to be ranked 1 and 2 in the sport. They transformed the game with their booming serves and punishing groundstrokes, and they parlayed their charisma into celebrity and clout previously unimaginable for female athletes.

"Not just for tennis, but for women's athletics, period -- they set a standard that was totally amazing," Garrison said. "Now we've seen more female athletes able to go on the covers of magazines they never thought of being on -- Glamour, Vogue -- and have all types of major endorsements."

The sisters' interests have broadened as they have matured. Venus runs an interior design company; Serena, 24, is dabbling in acting and designing a clothing line called "Aneres," which is Serena spelled backward. Together they starred in a reality series on ABC Family, "Venus and Serena: For Real."

Serena seems to particularly revel in the spotlight. In July she performed alongside Destiny's Child at the ESPY Awards. Venus has a lower public profile. She says she has spent the offseason working late nights designing swimwear for a project at the Art Institute of Fort Lauderdale, where she is studying fashion design. "I'm sort of tired," she said, "but it will pay off one day."

While some blame such pursuits for the sisters' slide in the rankings, Garrison thinks they are often judged too harshly.

"They have been on top for so long, and now they're 10th and 11th in the world," Garrison said. "We act like, as a country, that there's something wrong with this. Some people never make it to No. 10. They were so dominant. We should allow people sometimes to just go through some things."

Still, women's tennis hasn't been the same since the Williams sisters stopped dominating. Russian teenager Maria Sharapova captured the public's fancy after vanquishing Serena to win Wimbledon in 2004 and immediately landed endorsement deals with Canon and Motorola. But injuries have prevented her from ruling the sport, as they have Justine Henin-Hardenne, Kim Clijsters and the sisters.

That revolving door at the top is probably why Martina Hingis, 22, announced recently that she would return to the pro tour after a three-year absence, said ESPN commentator Mary Carillo. "No one in women's tennis is showing endurance. No one -- including the Williams sisters," Carillo said. Carillo hopes fervently that the 2006 season sees the Williams's roar back.

"I do think the Williams sisters have to re-declare themselves and say, 'Here's who I am,' and 'Here's what I want,' " Carillo said. "These people are supposed to be fixtures in women's tennis; not shooting stars. They're already in the Hall of Fame. They have made history. But I thought they were going to make continual, lasting history. If they felt like, they could be No. 1 and No. 2 in the world again."

Serena, left, and Venus Williams have become more than just tennis players. "They set a standard that was totally amazing," Zina Garrison said.