The cost of Arlington County’s planned indoor swimming pool and fitness complex has ballooned by millions of dollars in the past month, causing officials to consider downsizing, delaying or discarding plans for the facility.

The Long Bridge Park aquatics center would be built on a sliver of reclaimed land between freeways and railroad tracks in Crystal City. It was supposed to be a crowning achievement of a county that prides itself on planning and fiscal prudence.

But County Manager Barbara Donnellan put a hold on the project Jan. 3 when construction bids came in “significantly higher” than the $79.3 million that had been expected. And county staff acknowledged last week that the cost of operating the complex has doubled to $3.8 million per year.

The center would feature an Olympic-size competition pool, a teaching pool, a family leisure pool with slides and a “lazy river,” an indoor fitness area and eight acres of outdoor space. A popular esplanade that already is in use would be expanded, and eight acres of new parkland would be designed as spaces for festivals and large gatherings.

Concern about the aquatics center comes less than a year after the county spent $1 million in local and federal money to build a Columbia Pike bus stop. That sparked a public outcry from residents, and the county has delayed construction of 23 additional shelters that would have cost about $950,000 each; a consultant’s report on how to trim that cost is overdue.

And now some county officials are worried that with the worst of the recession over, construction companies no longer have reason to keep their costs low, which could mean higher prices for public works projects.

In the next 10 days, bids are due for turning a portion of an Arlington office building in the Courthouse neighborhood into a 24-hour homeless services center and shelter.

Other major construction projects coming up include the Columbia Pike and Crystal City streetcar lines, a new Williamsburg elementary school and a variety of maintenance projects that, taken together, add up to a major expense. The county also is getting close to its self-imposed rule that allows only 10 percent of its operating budget to be dedicated to debt service, which could limit its spending.

Donnellan’s decision to delay awarding the aquatics center bids and reexamine the costs drew support from County Board Chairman Jay Fisette (D) and Vice Chairman Mary H. Hynes (D), but for different reasons.

“I am hopeful we can find a way to responsibly move forward,” said Fisette, the board’s major supporter of a new aquatics center. “I know there are people who don’t support the park or the facility, but some of their [rhetoric] is wildly exaggerated.”

Hynes, however, said she wanted to keep “all the options” open as to the future of the aquatics center. She said that not enough money is available in the capital budget to spend much more on construction for an aquatics center and that she doesn’t support increasing taxes to pay for it.

Hynes also expressed concern about the projected ongoing operating cost, comparing it to the money-losing Artisphere, an art gallery partially owned by the county.

“Operations for pools are always expensive. They’re money- sucks,” she said. “I told the manager last spring that you have to convince me that the business plan [to operate the center] is workable. . . . I’ve been very conservative about how these stand-alone singletons are going to work.”

It’s unclear why the aquatics center bids came in so much higher than the county architect had expected, especially since Arlington hired an outside engineering firm to review the documents and make a separate cost estimate.

The operating cost, first estimated in July 2012, rose after final drawings for the facility were completed, said Jane Rudolph, the director of parks and recreation. The number of lifeguards and maintenance workers increased. The first estimates did not take into account how the cost would increase over time, which pushed up the estimate by as much as a half-million dollars as well.

Rentals and fees are expected to generate between $2.75 million and $3.4 million. But most of the money to pay for the aquatics center comes from two bond referendums approved by c ounty voters and $15 million from the real estate company Vornado Realty Trust, the county’s biggest taxpayer, as part of a deal that allowed the construction of the nearby PenPlace commercial development.

The most recent bond referendum for parks, which included the construction of the aquatics center, passed with 64 percent of the vote in November 2012.

Proponents, including enthusiastic members of Arlington swim clubs, said existing pools are small and overcrowded. In addition, demand is high for recreation and open space in the nearby Crystal City and Pentagon City neighborhoods.