The D.C. Builders Association will sponsor a program on commercial revitalization of urban neighborhoods Monday evening at the National Housing Center, 15th and M streets NW. John Sower, director of the National Development Council, will be the speaker. For information, call 966-8665.

A seminar on historic preservation in the District will be held from 2 to 5 p.m. Wednesday at the National Housing Center. The Washington Board of Realtors is the sponsor. For information, call 622-4494.

The Montgomery County Board of Realtors has opposed proposed country legilsation that would impose a tax ($3.70 per $100 assessed valuation) on the differences between assessed valuation and 45 per cent for the sales prices, with an exemption for the first $5,000 of the difference. Based on this formula, a home assessed at $20,000 ($40,000 value on basis of assessment) and selling for $60,000 today would be taxes an additional $74 at the time of transfer.

The Maryland Association of Realtors will hold its annual convention June 16-18 at the Convention Hall in Ocean City.

A seminar on apartment rehabilitation will be held Wednesday at the Ramada Inn in Lanham under the sponsorship of Chapter 8 of the Institute of Real Estate Management. Information is available by calling 474-6207.

Hugh B. Robey has been named director of parks and recreation in Prince George's County and Barry D. Mangum deputy director.

William J. Hatch has been named vice president of development services for Gulf Reston, Inc., and William B. Moore Reston's vice president of operations.