Architect Michael Steiner will present a day-long seminar on solar energy next Saturday on the Loudoun campus of Northern Virginia Community College. The workshop is designed to aid homeowners interested in incorporating solar energy into their homes. The registration fee is $10 or $15 a couple. For information call 323-4551.

Thomas Hamilton, executive of the office of landlord-tenant affairs in Montgomery County, will be the speaker Tuesday evening when the Montgomery chapter of the National Society of Residents Managers meets at the Holiday Inn in Bethesda.

Schwartz & Co., which is developing contemporary houses in the $172,000 plus range in Saddle Ridge of Potomac, has introduced a new model that has 6,600 square feet of living area.

Home builders from Southern Maryland will meet Tuesday evening at the Hawthorne Country Club in LaPlata. Gary Mall of the Maryland Forestry Service will be the speaker.

The area chapter of the Mortgage Bankers Association will meet at noon Monday at the Mayflower to hear Vernon George, an economic consultant.

The Montgomery County Board of Realtors reported that it had 20,200 residences listed for sale in its multiple listing service in 1977, compared with 7,184 a decade earlier.