Stan Kasten is leaving the Washington Nationals after 4½ years as team president, announcing Thursday that he will resign at the end of the season.

Kasten did not explain in detail exactly why he decided to depart.

"It's just time to be doing something else," Kasten said.

The Nationals are headed toward a third consecutive last-place finish in the NL East,and their attendance is 14th in the 16-team league.

Washington's game against Houston on Monday drew an announced paid attendance of 10,999, its smallest at Nationals Park since baseball returned to the nation's capital in 2005. Fewer than 12,000 showed up Tuesday, and under 13,000 were at Wednesday's game at a stadium that opened in 2008 and holds more than 40,000.

"The decision for me to leave was not hard. It was the right thing to do," Kasten said.

In May 2006, Kasten was part of the group led by Washington-area real estate developer Ted Lerner that was picked by Major League Baseball to buy the Nationals.

"I made a commitment to stay with them for five years — through the end of the 2010 season. About a year ago or so I went to the family and told them I would not be staying beyond that five-year commitment," Kasten said.

Kasten immediately became the public face of that group, doing most of the speaking at a news conference to introduce the new owners.

Kasten said Lerner and his brother, Mark, wanted him to stay with the team.

"I had great relationships with the Lerners. We had really good talks. This was clear this was what I wanted to do. Yes, they would have been happy for me to stay," Kasten said.

In a statement, Ted Lerner said: "Stan Kasten will always be an important part of the history of the Washington Nationals. He was vital to ownership winning its bid from Major League Baseball."

"Over his tenure he has positioned the Nationals to become one of the most exciting franchises in baseball and we thank him for all that he has accomplished," Lerner said.

He also declined to say whether he would retain his ownership stake in the Nationals.

"I know the stories and speculation. Let me assure you, this is just about me. This has nothing to do with anybody else or anything else," Kasten said. "This is about me, what's good for me and my family and my own personal expectations, goals, aspirations, purely that and nothing else."

He also said he doesn't know what he's going to do next.

"I can't know that I'll do this again. I don't feel like retiring," Kasten said. "I don't think you'll lose track of me."

When he came to Washington, Kasten immediately outlined the plan he wanted to implement to improve the club, focusing on pitching and grooming young talent. He hoped to create success similar to that of the Atlanta Braves, who won a World Series championship and 14 consecutive division titles after Kasten oversaw their rebuilding.

While the Nationals organization made some strides in improving its crop of minor league players, the big league team has struggled to be competitive. The Nationals finished with the worst record in the majors in 2008 (59-102) and 2009 (59-103), which allowed the team to be the first in baseball history to have the No. 1 pick in the amateur draft two years in a row.

"Until we win it all, I don't have any crowning achievements," Kasten said.

The Nationals picked Stephen Strasburg in 2009, signing him to a record $15.1 million contract, and he made his major league debut to much fanfare this June. But the right-handed pitcher was injured last month and he had reconstructive elbow surgery on Sept. 3 that could keep him out of the starting rotation until the 2012 season.

About two hours after Kasten announced his resignation and lauded fans for attending despite the team's poor record, the Nationals said no season ticket prices would be raised in 2011. Also, the three most expensive categories will be reduced.

Kasten was a powerful figure on the Atlanta sports scene for more than two decades, running baseball's Braves, the NBA's Hawks and the NHL's Thrashers. He left all three posts in November 2003, when the Hawks and Thrashers were on the verge of being sold to new owners and the Braves were going through budget cuts.