Northern Virginia's third-largest and perhaps most politically influential law firm will merge with a Winchester, Va., firm to expand its reach in the state.

Hazel, Thomas, Fiske, Weiner, Beckhorn & Hanes -- the firm founded by developer John T. "Til" Hazel -- will merge on July 1 with Costello, Dickinson, Johnston, Greenlee, Coleman & McLoughlin, a Winchester firm with specialties in real estate law and tax planning.

The combined firm will have about 155 attorneys.

Duane W. Beckhorn, one of the named partners in the Hazel, Thomas firm, which has 145 attorneys, said the merger with the smaller firm would give Hazel, Thomas a foothold in the Shenandoah Valley, where manufacturing and agricultural industries are growing.

John T. Hazel is also a partner in the Hazel/Peterson Cos., the aggressive development firm that tried to build the William Center shopping mall near the Manassas battlefield park several years ago. The federal government eventually stepped in to buy the land to prevent it from being developed.

Another partner, William G. Thomas, is a prominent lobbyist in Richmond and a fund-raiser for Virginia Democrats.

The Hazel, Thomas firm specializes in white-collar crime and civil litigation, real estate law and bankruptcy.

Beckhorn said yesterday that some of the firm's practice has been changing because of the beating that the real estate industry is taking in the Washington area. Because there are few new construction deals going on, the firm has turned to doing more business with troubled companies that are attempting to avoid bankruptcy.

The merged firm will have seven offices in Virginia, Maryland and the District.

The firm will be known as Hazel & Thomas, Beckhorn said, "because we thought the other name was too long."