Jack and Marty Shoff of Silver Spring had almost given up hope of finding a home they could afford -- the $20,000 a year makes as a medical social worker just didn't seem to meet the high stakes of the Montgomery County real estate game where the average cost of houses is well over $90,000.

But Monday night their lucky number came up at the county's housing lottery and with it the chance to buy a new townhouse in the heart of affluent Potomac for about half the market price.

"It's just hard to believe," said Mary, 27, a 2-year-old daughter squirming in her arms. "I called the housing office today because I wanted to know the percentages. They told me they were 24 to one."

The Shoffs, who also have a 17-month-old son, were among the more 500 hopeful families and single persons whose names were placed in a fishbowl at the county office building. Being offered in the lottery were chances to purchase 14 townhouses in Potomac's Falls Reach subdivision at Tuckerman Lane and Falls Road, and in Silver Spring's Beacon Place subdivision at Bell Pre Layhill roads.

Since 1978, more than 900 families have been placed in homes under the Montgomery's moderately priced dwelling unit program which requires developers who build more than 50 housing units to make 15 percent of those homes or condominiums available at reduced prices. Those selected as potential purchasers of the new homes may also apply for low-interest financing.

To the Shoffs, whose names have been on the housing office waiting list of 3,500 persons since Janurary, the lottery meant the opportunity to purchase a three-bedroom home in Potomac -- an area where they would not have otherwise been able to afford a house -- for $51,941.

"We've had units sort of on the border of Potomac and Bethesda," said program planner Glenn Kreger, "but these are the first in Potomac proper." Kerger is not certain what the market price of the townhouses will be once they go on sale next year, but estimates they will bring almost double the price the Shoffs will pay.

The county holds lotteries whenever the developers have housing units available. Over the summer, there have been 14 lotteries for new home and rental housing throughout the county.

The Shoffs new rent a two-bedroom condomimium in Silver Spring. As their son and daughter grow older, they say, they will need more space. Potomac appeals to them because of the quality of its schools, the high resale value of houses and proximity of Mary's parents, who live in Potomac.

"This area is exteremly expensive for a young family getting started," said Jack, 28. "We really weren't looking much because we couldn't afford much."

Jamie and Kim Williams of Gaithersburg were not as fortunate as the Shoffs. A contruction manager in Washington, Jamie makes approximately $20,000 a year to support his wife and 2-year-old son, Jed. They say they would like to move from their small, two-bedroom apartment in Gaithersburg, which they rent for $307 a month.

"If it weren't for this program we couldn't afford to buy," says Jamie, 23.

"The HFC (Household Finance Corporation) financing figures out to a savings of about $200 a month."

Although persons are not required to be present during the drawing to win the opportunity to buy or rent, the auditorium is nearly always filled when the lotteries are held. On Monday, appoximately 150 persons -- primarialy young families -- were present. Of those, only two families were present to witness their names drawn from the fishbowl. Many stayed to ask questions afterwards, but the majority went home disappointed.

The Williams say they will keep their names on the list and continue to review the lists of homes to raffled that they receive sporadically from the housing office. We're somewhat disappointed," says Jamie, as Kim smiles and adds, "but something will come up."