After a long day on the golf course, Cristie Kerr relaxed on a cushioned seat opposite her husband, Erik Stevens, and savored every moment of an orange sherbet sunset from the patio of the Mirabel clubhouse, a quick cart ride from their home in North Scottsdale, Ariz.

They gazed beyond the 18th green, where they were married in December 2006, into a future they figured would have arrived by now.

Every day, Stevens said, they talk about starting a family. At 45, he gets paternal pangs watching a television commercial with a father frolicking with his children, but is careful not to press Kerr about having a baby.

“There’s a little pressure on her,” he said. “The L.P.G.A. needs its stars right now.”

For Kerr, the impediment to motherhood is golf, and there is no automatic relief. A woman’s athletic prime and her peak child-bearing years overlap like a total eclipse of the moon. A woman’s fertility peaks in her mid-20s and declines sharply after the age of 35, a real conundrum for golfers, whose games, like the courses they play, take years to mature.

“I really feel like I can be No. 1 in the world,” Kerr, 32, said before this season. “I feel like I’m just coming into my golfing prime. I’m just starting to be in the best shape of my life.”

In June, Kerr ascended to No. 1. She enters this week’s United States Open at Oakmont Country Club in Pittsburgh as the first American atop the world rankings since they were formally established in 2006. With one lifelong goal achieved, will Kerr soon shift her focus?

Over the past two years, the L.P.G.A. Tour’s two biggest stars retired to devote their energies to family. The departures of Annika Sorenstam at 38 and Lorena Ochoa at 28 rocked a tour that was reeling from lost sponsors and tournaments.

In this age of million-dollar purses and million-mile travel, can the L.P.G.A. keep its superstars long enough to increase the tour’s following? The players’ fitness trailer is a reminder of the tour’s weakened state; its sides are adorned with larger-than-life images of Sorenstam and Ochoa.

Michael Whan, the L.P.G.A. commissioner, said women’s professional golf was “a tough, aggressive, highly paid career path, and people struggle with what kind of competitor they want to be and what kind of mom they want to be.”

He added, “We try to make it possible to be a mom and be competitive, but we can’t make it where nobody leaves because, quite frankly, that’s personal choice.”

The tour, Whan said, will always have women who leave “because their next quest in life is to be home and have a family.”

The tour offers free day care for domestic events, but players like Kerr see only the balls to be juggled and not the helping hands.

At a May tournament in Mobile, Ala., Kerr exchanged a hurried greeting with Karen Stupples, who was rushing to retrieve her 3-year-old son from the tour’s day care center 15 miles away. Kerr glanced at her husband, and the thought that passed between them, Stevens said, was, “No way can we do that!”

Conversations on motherhood among golfers now often include surrogacy, adoption, freezing eggs, assisted reproduction techniques and the side effects of hormone injections.

When Nancy Lopez was dominating the tour in the early 1980s, such discussions began and ended with finding and affording child care.

“It’s definitely different for women,” she said. “Guys, they have a wife who takes care of the children. They can focus totally on golf.”

Lopez’s plan was to retire in 1983 when she became pregnant with the first of her three daughters.

“But I really cared about helping carry the tour to wherever I was supposed to carry it,” she said. “It was my obligation, I felt, to keep playing.”

Lopez, now 53, won 21 of her 48 L.P.G.A. titles as a mother.

“Women are multitaskers, I just believe that,” she said in June at a tour event in Springfield, Ill., where she was a guest. “Lorena, Annika, they’re both tough. I think they could have done it.”

Juli Inkster, who won four of her seven major titles after the 1994 birth of the second of her two daughters, does not seem so sure.

The globalization of women’s golf has raised not only the level of play and the purses, but also the stakes for having children. So far this year, four L.P.G.A. tournaments have taken place outside the United States, with two more in Europe this month.

Inkster, who turned 50 in June, said, “I think if our tour goes more international, if you want to be a hands-on mom, it would be really hard to do both.”

The travel, which was always hard on Ochoa, grew unbearable after her December marriage to Andrés Conesa, the chief executive of Aeroméxico, who had three children with his first wife. Ochoa returned home from season-opening events in Thailand and Singapore and told Conesa she would quit in May.

“Andrés asked me, ‘Did I have something to do with this?’ ” Ochoa said. “I told him, ‘Only because I’m with you and I’m happy.’ I think my retirement was hardest on Andrés. He feels some blame, I guess, because people see that I got married and now I’m quitting.”

As she spoke, Ochoa was seated in the women’s lounge at Guadalajara Country Club, where she learned to play and returned for a tournament to benefit her charitable foundation. She was surrounded by three generations of female relatives, including two toddler nieces whom she entertained effortlessly.

It was clear the golfing world had framed her retirement all wrong. The pertinent question was not how she could leave before fulfilling her 10-year requirement for L.P.G.A. Hall of Fame eligibility, but how did she last eight full years on the tour?

“This is true,” she said. “I was in Thailand, and I was thinking, I’m going to try really hard to focus on golf, and I’m going to lose valuable years of my life, and what for? So I can win maybe four more tournaments? I want to live a more-normal life. I want to spend time with my family and not miss the important events like birthdays and baptisms.”

Ochoa had accomplished all her goals in golf, as had Sorenstam, who won 10 majors and earned more than $22 million. Last year, Sorenstam married Mike McGee and gave birth to a daughter.

“Growing up, sports was my passion, and I wanted to have a career,” Sorenstam said. “I saw the friends that had children, but to me, that wasn’t the first thing that I wanted to achieve. But once I achieved more and more on the golf course and got older, I guess, I started realizing I’m happy with my career, and now it’s time for another chapter.”

Asked if she worried that she might have waited too long to start a family, Sorenstam replied: “Of course. That’s a very natural thing. You’re not older than you feel, and so you keep on going and all of the sudden you go, ‘Oh, I’m getting up there,’ and you’ve got to start thinking about things.”

For Kerr, the toughest course to plot a strategy for is motherhood.

“Some people get pregnant right away,” she said. “For some, it takes years. How do you know what’s going to happen? What if I couldn’t have kids and I need a surrogate? What if you wait until your late 30s and you can’t conceive?

“Are you going to be the natural mother? Are you going to adopt a baby? Are you going to have a surrogate?”

She and Stevens, a marketing consultant who is Kerr’s agent, routinely discuss those questions.

“Cristie earns $1 million a year on the golf course,” Stevens said. “If she’s going to shut herself down for six months, what is that going to mean for the business? And the second part of it is, What’s going to happen after the pregnancy? What’s it going to do to her career? If Cristie wants to be involved in every aspect of parenthood, how will that absorb her time?”

Kerr was overweight as a teenager and shed 60 pounds from her 5-foot-3 ½ frame in two years after turning pro in 1999. She has to be vigilant to maintain her size 2 figure, and worries that she will not be able to lose pregnancy weight, she said.

“I’ve definitely done the investigative work,” Kerr said. “It’s almost like getting a surrogate would be the logical option for us. But I’m such a control freak, I don’t know if I could have a surrogate.”

She added, “I honestly thought I would have become a parent by now.”

Kerr took a sip of wine and put her glass down gently.

“Some things,” she said, “you can’t foresee.”