With every sign bannered conspicuously on an apartment building -- Condominiums for Sale -- renters are uprooted and move elsewhere, new owners arrive and the community's population undergoes an abrupt change.

To learn more about uprooted apartment dwellers, new condominium owners and the net effect on its population, Montgomery County hired the Baltimore consulting firm Hollander Cohen Associates Inc. to contact former tenants and new residents of seven apartment buildings that were converted to condominiums in early 1979.

A preliminary draft report says the new inhabitants were younger and earned more money, the displaced tenants had larger families and smaller incomes, and those affected most adversely were elderly tenants. Local officials find none of those conclusions surprising.

But the findings were also critical of county agencies. The report said although the majority of the tenants experienced no apparent hardship and most were accommodated by the housing market, the plight of elderly renters was severe. It said the county's efforts to help tenants were fragmented and of "indifferent merit."

"One-tenth of those interviewed acknowledged asking for help from the Montgomery County Housing Informatin Center or any other agency. Only a minority of those said they got the help they asked for," the draft said.

The study covered Bethesda Park, Grosvenor Park, Kenwood, Park Sutton, Rock Creek, Top of the Park and The Wellington. Findings varied considerably among the buildings, with a higher percentage of people buying their apartments in a less expensive building. Of the 2,000 apartments in all the buildings that had been sold by the time the study was conducted this year, 43 percent were occupied by new owners and 35 percent by former tenants.

The remaining apartments, 22 percent of the total, were purchased as investments and rented out, sometimes to the building's former tenants.

Thomas and Dorothea Doughty are such renters. After looking at more than 30 buildings at the time of Kenwood's conversion, they settled on what they considered the only conversion-proof solution: renting an investor-owned apartment in the converted building.

"We casted around. We tried to play the game of finding where we would be safe. We tried to pick the county or municipality where we'd be the safest renting," said Thomas Doughty, a retired Export-Import Bank employe. "But whenever we found something we liked, we had to reject it because it was a perfect target for conversion."

"If we had panicked and moved out, we'd have moved to someplace that now is condominium," he said.

The study found that 82 percent of the displaced tenants stayed in Montgomery County, 12 percent stayed in the Washington metropolitan area and 5 percent moved out of town (1 percent did not respond to the survey). Of the new occupants of the condominium buildings, 72 percent are from the county, 19 percent from the area and 9 percent from out of town.

A converted building has many more young singles, and more people with annual incomes exceeding $30,000 or assets of more than $25,000. Only 2 percent of the former tenants who bought their apartments had children. The vast majority of the displaced tenants -- 76 percent -- continued as renters elsewhere, but most were less satisfied with their new apartments.

Asked why they didn't buy, 41 percent said they could not afford to, 27 percent said the unit was overpriced and 20 percent said the building was in poor condition. Others cited a dislike of condominiums, an aversion to owning, or said they were elderly and did not want to buy.

Robert Young, who bought one of the apartments in The Wellington, is typical of new condominium owners in that he is young, single and earns more than $30,000 a year. He rented a house with two other men for a few years, but as a successful sales agent for a real estate firm, he was looking for a chance to buy a small apartment.

"When you're in real estate, you eventually succumb to the mentality of leveraging your money," said Young, who was attracted by the renovation of the 30-year-old Wellington apartments. His kitchen was new, complete with microwave oven and dishwasher, and the apartment cost $49,500. Today, he said, he could sell it for $63,000.

At about the time Young was born, Elsie Moore moved into The Wellington. A Montgomery County schoolteacher, she was delighted with her new apartment, which then rented for $89 a month. The location, on Strathmore Drive a block from Wisconsin Avenue, was superb.

She lived there for 30 years. But then it went condominium and she "just didn't have the money" to buy, she said. She found an apartment at the Glen Aldon, a short distance away on Battery Lane. But her rent will be $400 this September, compared with the $168 she paid at the Wellington.

The cost of housing increases for everyone concerned when a building is converted, the study found. Those who find unconverted apartment buildings pay the slightly higher rents of a shrinking rental market. People like the Doughtys, renting from an investor, pay 20 to 30 percent more and those who the units must pay condominium fees and mortgage payments that are sometimes double their previous rent.

"Oh yes, it stirred up quite a big furor," said Thomas Doughty, reflecting on the conversion of the Kenwood. "When the notices came out, many of the tenants were widows who had just sold a house and wanted to rent. Some moved to Grosvenor or the Promenade, and the next thing you know they got condo notices and had to get out of there."

Doughty remains a committed renter, even if it means 30 percent more in rent for an apartment in the same building. "To buy into this sort of thing would be like living in a gilded cage. We would have no money to go to the Kennedy Center.All our money would be tied up."

"Our friends were scattered like ants," said Dorothea Doughty. "I think what's being done to old people cries to the heavens."