James K. Hartmann, Alexandria's city manager for six years, made his resignation official Monday afternoon.

Hartmann, 57, said he wants to pursue job opportunities with a focus on Florida, including a county manager position in Seminole County.

"I was ready to pursue other career challenges and . . . because it will be a very open environment, I thought it was best to close out this chapter as I'm building the next one," Hartmann said.

After eight years in the U.S. Coast Guard, Hartmann worked in Orange County, Fla., for 13 years. His wife is originally from Orlando.

Hartmann also worked as a county administrator in Eagle County, Colo., and Spartanburg County, S.C. He told Alexandria officials of his intentions at the City Council meeting Jan. 25.

That "came as a total surprise and shock to all of us," said Mayor William D. Euille (D), who said council members persuaded Hartmann to stay beyond his required 90 days until the fiscal 2012 budget is adopted May 2.

"We got six good years out of him. He met the mandates we set for him," said Euille, who listed budget cost-cutting and making city and business operations more efficient among Hartmann's accomplishments.

Euille said Hartmann's "success here in Alexandria certainly raised our profile and visibility on a national arena or scale" and could lead to other municipalities to "come calling" for Hartmann's services, he said.

The city is in the midst of transforming Potomac Yard into a multi-billion dollar development with a new Metro station, increasing commercial projects along Eisenhower Avenue and conducting several transit studies, among other projects.

The majority of those projects have been planned, Hartmann said.

"If they stay true to the plan, they will be great places," he said. "I think sometimes the planning is important, if not more important, than the execution of it."

As for Hartmann's decision to announce his departure now, he said, "There is never a time when it all stops. It is always going to be a huge work in progress. I feel the timing right now is very good, and this organization is very capable of handling a transition."

Applications for the Seminole county manager position were due Monday, according to the Florida Association of Counties Web site.

Seminole is about 345 square miles between Orlando and Daytona Beach, with a population of 425,000. The county's 2009-10 budget was about $885.4 million, and it employs 1,325 people, according to the site.

Alexandria, in comparison, is about 15.75 square miles and has an estimated population of 145,000. The city's fiscal 2011 budget is about 531.6 million, and it employs about 2,500 people.

Council members will discuss and announce a search process for the next city manager in the coming weeks.