The nonprofit Loudoun Healthcare Inc. will announce today its decision to merge with the Inova Health System, a move that could allow the only hospital in the nation's fastest-growing county to greatly expand its services and remain competitive with a second, for-profit hospital being planned nearby.

Rod Huebbers, president and chief executive of Loudoun Healthcare, which runs the 92-year-old Loudoun Hospital Center, said the merger would bring better medical care to the county, where officials have said population growth is outstripping access to health care.

"What we're going to do is become an advanced community hospital," Huebbers said. "We've created a better health care environment for the future."

Under the terms of the merger, Inova has pledged $200 million to upgrade hospital services, build four smaller health centers across the county and construct an urgent care center on Route 50 south of Dulles Airport with the intention of turning it into a full-service hospital in the future.

The planned service expansions also include the construction of heart and cancer centers at the hospital's main Lansdowne campus in eastern Loudoun, the addition of 30 patient beds at the downtown Leesburg campus and the establishment of a research and training facility.

Inova, one of Virginia's largest nonprofit health care systems, will now run six hospitals. J. Knox Singleton, Inova's president and chief executive, said the merger with Loudoun Healthcare is "a logical marriage" that will give Inova the chance to expand its research activities while providing Loudoun residents with advanced health care close to home.

"There was really a great synergy when we put our efforts together," Singleton said. "This was really a win-win for the community."

The merger is the latest twist in a struggle over the future of health care in Loudoun County, where hospital officials have fought the arrival of Nashville-based HCA, the country's largest for-profit hospital chain. HCA received state permission in March to build a 164-bed hospital in Loudoun and is awaiting county approval.

Loudoun Healthcare says the HCA facility, to be built just five miles from Loudoun Hospital's Lansdowne campus, would drive up health care costs by forcing the two facilities to compete for patients and doctors. HCA argues that the county's booming population can support two hospitals and that residents would benefit from competition brought by its new Broadlands Regional Medical Center, which is scheduled to open in 2008.

Huebbers said yesterday that the merger "has got nothing to do with Broadlands." Tony Raker, a spokesman for Loudoun Healthcare, said the merger "will definitely keep us strong."

Megan Descutner, a spokeswoman for Broadlands, said it is too early to know whether Loudoun Hospital's plans to expand -- which would require the county's approval -- will affect business at Broadlands.

"This doesn't worry us," Descutner said. "We are so far ahead in this process . . . we need health care as soon as possible."