Ryan Homes recently agreed to pay $300 each to 20 Montgomery County homebuyers whose two-car driveways had concrete aprons large enough for only one car, according to the Montgomery County Office of Consumer Affairs.

The Pennsylvania home building corporation, with local offices in Rockville, signed a cease and desist agreement with the consumer affairs office, which says it failed to disclose to prospective buyers a narrow driveway apron that caused homeowners to drive on their own lawns.

When the company first started selling homes late in 1976 at its North Orchard Manor subdivision in Gaithersburg, no driveways were in place at their model homes for buyers to see. The Office of Consumer Affairs said Ryan should have informed purchasers of such homes beforehand that they would get only a one-car-wide apron.

The agreement said that some homeowners complained that the resulting damage to the property reduces the fair market value of their homes. Ryan Homes denied the allegations and denied violating the full disclosure provisions of the county's consumer protection law. But the firm agreed to pay homebuyers who contracted to buy before March 15, 1977 when the first driveways were poured, and who went to settlement before July l of that year.