The two-building Century Plaza office complex in Columbia has been sold to Grosvenor Properties Ltd, a partnership of Robert K. and Donald Werbe of San Francisco, Equitable Life of Iowa, which devloped the 160,000-square-foot property five years ago for a reported $12 million, was the seller. The Werbes also own the Grosvenor Riverside in Alexandria.

St. Richard's Manor, a 300-year-old home on 56 acres on the Patuxent River in St. Marys County, Md., was sold recently to George and Lisa Donely of Washington, according to Mark IV Associates. Donely is an economist with the International Monetary Fund. Attorney George T. Daughtery of Lexington Park was the seller.

Both Kettler Brothers Inc. and Edw. R. Carr & Associates recently enrolled their 1,000th homes in the Home Owners Warranty program sponsored by area builder associations. Both firms gaves presents to their 1,000th HOW buyers.

The Property Management Association and the Apartment and Office Building Association will hold a trade show Oct. 12 at the Capital Centre.

A three-part home improvement course will be held Oct. 4, 11 and 18 by the Montgomery County Office of Consumer Affairs. Evening classes will be held in the Twinbrook Library on Meadow Hall Drive. For information dial, 279-1776.

Walker & Dunlop has arranged permanent fiancing of $900,000 for the Fullerton industrial building in Fairfax County. The loan on the one-story, 54,000-square-foot building developed by John E. McPHerson Jr. was placed with Great-West Life Assurance Co. of Canada.

The National Center for Housing Management has arranged a national conference on management of HUD-assisted housing to be held Oct. 23-25 at the Pentagon City Quality Inn. To reserve, dial 872-1717.

The new headquarters building of the United Fresh Fruit & Vegetable Association will be dedicated at 2 p.m. Tuesday at 727 N. Washington St., Alexandria. The association will use two of the building's three floors. The UFFVA now is in a downtown Washington location. The new stracture, to be occupied in mid-October, was built by Eugene Simpson and Brother Inc.

Columbia Technical Insitute in Arlington has begun its fall classes in construction and related courses, including a special course in building blueprint reading and estimating. Information about the evening classes is available by dialing 920-8866.

Gibson Realty and Management Co. Inc. has announced that the Veterans Administration will take more than 100,000 square feet of warehouse space in a new building in the Fleet Industrial Park in the Franconia-Springfield area.

The area Mortage Bankers Association and the area Land Title Association will hold a seminar on title insurance Monday at the Sheraton-Lanham and on Friday at the Ramada Key Bridge. For information, dial 223-0297.

The 11th annual Dupont Circle house tour will he held Oct. 15 from 1 to 5 p.m. by the Dupont Circle Citizens Association. Eleven restored and renovated houses in the newly established 16th Street Historic District will be shown. For information, dial 387-5312.

A.J. Dwoskin & Associates Inc. of Fairfax has announced that Kmart has signed a lease for 84,000 square feet in a new facility to be built on the north-west corner of Lee Highway and Jermantown Road in the City of Fairfax. Other commercial facilities will be built in the complex for which Dennis Galanis of the Dwoskin firm is handling leasing.