The Willard Office Building, built as a part of the Willard Hotel restoration project, was completed last week and is already two-thirds leased, according to the developer, The Oliver T. Carr Co.

The 250,000-square-foot building, located on Pennsylvania Avenue between the White House and the Capitol, was built adjacent to the original Willard Hotel, which is under renovation. It provides 218,600 square feet of office space overlooking the Mall and many historic monuments.

Tenants are paying "above $35 a foot" for space in the building, a Carr spokesman said.

The three major tenants are: Vinson & Elkins, a Houston law firm, leasing 54,000 square feet; Hale and Dorr, a Boston law firm, leasing 24,600 square feet; and Davis & Harman, a local law firm, leasing 14,400 square feet.

The old Occidental Restaurant will be recreated on the first three levels of the building, and the Willard Collection of Shops will consist of 20 boutiques and restaurants occupying another 24,700 square feet. The retail section will open onto a plaza with fountains and greenery on Pennsylvania Avenue.

Other recent developments in commercial realty in the Washington metropolitan area:

*Eight companies have leased space at the 128,000-square-foot Twelve Oaks Office Park on Research Boulevard in Montgomery County. The leases have a total value of $7 million. Marriott Corp. was the largest lessee with 72,000 square feet; IBM Corp. was second with a renewed and expanded lease of 37,000 square feet.

*Miller and Smith Commercial broke ground on the third building in the Hartland Business Center at 2735 Hartland Rd. in Merrifield, Va.