YELLOWSTONE NATIONAL PARK (AP) - Rising prices for building materials and a tight labor market have put a number of construction projects on hold here, and park officials have returned to the drawing board to see if they can make them less expensive.

Among the projects is a proposed visitor center at Old Faithful, and a new wastewater treatment plant at the park's Madison Junction.

Park officials say the first hints of potential problems came in August 2005, when bids for two projects were 30 percent to 50 percent higher than anticipated.

"That's when we knew were in trouble," said Steve Iobst, Yellowstone's chief of maintenance,

Officials encountered similar problems last July, when they received just one bid for the Old Faithful visitor center. That $26 million bid also was higher than expected.

"It was way beyond the world of reality," Iobst said.

The same happened with the next phase of work on the historic Old Faithful Inn.

"We ran into a bidding market buzzsaw as well on that," Iobst said.

At a time when the park was expected to be buzzing with construction projects, it is relatively quiet, instead. Projects on hold are the two at Old Faithful, a new justice center at Mammoth Hot Springs, a new entrance station at the park's west gate, and the wastewater treatment plant.

Work on the $3.5 million plant, to replace one that park officials have said could see a "major failure" at any time, was supposed to start last summer.

The projects coincided with a dramatic rise in costs, especially for materials such as steel, concrete, copper and wood - much of it driven by international construction markets in China and India.

Meanwhile, construction in the region has been booming, especially in Montana's Gallatin and Flathead counties.

"It's been somewhat unprecedented in terms of the amount of construction in Montana," said Cary Hegreberg, director of the Montana Contractors' Association.

All of the activity means workers are hard to find and keep. Contractors are having particular difficulty finding workers who can pass a drug test, Hegreberg said.

"If someone can make $30 an hour in Phoenix or Las Vegas, they will move from Montana to those markets," he said.

Geography also works against Yellowstone. A major project at Old Faithful typically requires that workers live close by in temporary housing, away from home and families.

"If you can get a stable, steady job where you're home every night at 5 o'clock, why pull up stakes and go to Yellowstone National Park to build a new visitor center?" Hegreberg said.

Park officials are reluctant to ask Congress for more money to meet market demands, because "it isn't there to give," Iobst said.

Instead, they are trimming plans.

The new Old Faithful visitor center probably will be about 10,000 square feet smaller than the original design, said Mike Tuss, of Billings, Mont.-based CTA Architects Engineers, which has designed several of the park's latest additions.

Designers also have looked at using less expensive building materials and techniques.

"It's not going to have the visual impact and dynamics it would have had, but it's still going to be a very nice project," Tuss said.

Park officials are demolishing the current A-frame visitor center at Old Faithful and will use a temporary building until the new one is built.

The project is expected to go out for bid again sometime late this year, so construction can begin in the spring of 2008.

The next time around, park officials are hoping that more than one contractor bids on the project and is closer to home. A Kentucky firm was the sole bidder for the project last summer.

New bid proposals on the justice center and West Entrance projects are expected to go out this month.