Idexx Laboratories breaks ground today in Westbrook for a $35 million headquarters building, which the company in recent years had threatened to build elsewhere.

Members of Maine’s congressional delegation and Gov. Paul LePage are among those attending the 10 a.m. ceremony at the Five Star Industrial Park off Eisenhower Drive, the company’s home since 1991.

The 108,000-square-foot administrative building, which will hold offices for 300 employees, is the first half of a planned $60 million expansion, announced in July.

The timing of the second phase, a 100,000-square-foot building for 400 employees, will depend on the continued growth of the company, said facilities manager Dick Daigle.

“If we continue to grow at the rate we’re growing now, it’s going to be fairly quickly,” he said.

Idexx, which makes testing products for diagnosing diseases in animals and for determining the quality of milk and water, has expanded the number of employees in Westbrook from 800 to 1,800 in the past decade, said CEO Jonathan Ayers. The company employs about 5,000 people worldwide.

Plans for the corporate headquarters in Westbrook have been in the works for years, but were stalled in 2008 when Pike Industries announced its plans to expand nearby quarrying operations.

Idexx officials said at the time that, if Pike was allowed to move forward with its expansion, they would find a new place to build the headquarters.

Ayers said Monday they weren’t bluffing.

“We looked at a variety of sites in and around the surrounding area,” he said. “I actually walked some of the properties.”

Pike, Idexx and the city reached a consent agreement in 2010 that put limits on Pike’s ability to blast rock in its Spring Street quarry. Ayers said the compromise “allowed us to move forward.”

It did the same for Pike, which resumed blasting rock at the quarry in December.

Idexx officials said construction on the new building is scheduled for completion in August 2013.

The general contractor is Vermont-based PC Construction, which has an office in Portland. Lavallee Bresinger Architects of New Hampshire designed the building to Leadership in Energy and Environmental Design standards.

Daigle said some employees will move from the company’s existing building next door to the planned one, allowing all departments to expand. All of the company’s Westbrook employees will benefit from the new building, which will house a food service area and wellness center, offering the use of fitness equipment and health counseling.

“The jobs that Idexx provides are the ‘new economy’ jobs,” said City Councilor John O’Hara.

He said that during the Pike conflict, he was concerned “that Idexx could take these jobs and go anywhere in the world and be welcomed with open arms.”

That may be why the groundbreaking ceremony is drawing such high-profile attendees as the governor, U.S. Sen. Susan Collins and U.S. Reps. Chellie Pingree and Mike Michaud.

Adrienne Bennett, LePage’s press secretary, said the governor feels “it’s important for him to be a part of this.”

“It’s a local company,” she said. “It’s an investment in the state.”

Staff Writer Leslie Bridgers can be contacted at 791-6364 or at: [email protected]