Herndon-based software provider Deltek, which bought into the government contracting data and research market with an acquisition last year, made itself the dominant player in that market by buying its primary competitor last week.

The move is a big one for Deltek, which is best known for providing software to help contractors manage federal projects. Deltek has been rapidly rolling up companies since New York-based private-equity firm New Mountain Capital bought 75 percent of its shares in 2005.

Deltek said last week it paid $26 million in cash for market research and consulting company Washington Management Group, based in the District, and its Tysons Corner-based FedSources and FedSources Consulting businesses. The group, which has more than 900 clients and 20,000 users, had estimated revenue of $15 million in its most recent fiscal year, according to Deltek.

Last year, Deltek bought Reston-based Input, which competed against FedSources, for $60 million in cash and added Input’s nearly 200 employees.

“We were not looking at this as taking a competitor off the table at all,” said Deltek spokesman Patrick Smith. “We very much like the industry experts that FedSources has [and] there’s not a complete overlap at all in the databases.”

Kevin Plexico, senior vice president of research and analysis services at Input, said the acquisition adds consulting capabilities, expertise in more markets and about 500 new customers.

The Washington Management Group and FedSources locations will remain open, according to Smith. As part of the integration process, Deltek will evaluate whether to maintain the companies’ names.

Last year, Deltek picked up Danish firm Maconomy, which provides services to advertising, public relations, accounting and consulting firms, to expand its place in the global marketplace. Other recent acquisitions include Reston-based mySBX, an online network that allows government contractors and professionals to find partners and publish opportunities, and Planview’s MPM division, which makes project management software.