In the next 10 years, droves of baby boomers may be heading for the hills. And for the mountains. And for the beaches.

According to a new survey financed by the real estate and resort development industry, demand for second homes may surge in the 1990s as baby boomers move into the age group that typically buys vacation properties. Demand for vacation properties may soar from its current level of about 135,000 purchases a year to as many as 450,000 a year, according to the study's authors.

"Baby boomers generally are reaching that point in their lives where people historically have purchased vacation homes," said Steven S. Miner, research director of Eugene, Ore.-based Ragatz Associates Inc., which conducted the survey.

But the shift of development to the nation's hinterlands already is a matter of grave concern to environmentalists, who worry that more people and more traffic in once-pristine areas will damage wilderness areas.

Now, in a new twist, some are advocating that the federal government take a new look at the ways in which it is helping to accelerate the process.

A U.S. Forest Service report, based on public hearings and backed by environmental groups, has suggested that the federal government should reconsider the tax breaks it gives to people who buy vacation homes in such ecologically important areas as New England's Northern Forest.

"As a number of people mentioned, the federal tax provision to deduct the interest on second-home mortgages may encourage the demand for recreational development and could be partially responsible for the increased rate of land conversion threatening the Northern Forest," the report said. "While the purpose of the deduction is to stimulate growth and construction, it may be having other effects in the Northern Forest."

For many within the real estate industry, the mortgage-interest deduction is a key issue. Under current law, people who own second homes can deduct from their taxable incomes the mortgage interest they pay on the properties. In other words, depending on a household's tax bracket, the federal government will subsidize up to one-third of the cost of owning a vacation home.

The Northern Forest environmentalists are focusing on tax policy as a way to block development because the federal budget deficit means that little money is available to purchase land to protect it, said Mason Morfit, executive director of the Maine chapter of the Nature Conservancy, a group that buys environmentally endangered land to preserve it.

"In this day and age, money is so tight that we thought the federal government would be more willing to look at {changing} tax policy than at grants," Morfit said.

The idea of environmentalists tinkering with real estate-related tax policy is frightening to many in the real estate industry, who say that elimination of the mortgage interest deduction for second homes could prove catastrophic to resort developers and rural areas that rely on tourism dollars to survive. They say that without the mortgage interest deduction, many vacationers would rent rather than buy.

"This is a rather ludicrous proposal; it's so far-fetched it boggles my mind," said Chuck Houseman, sales manager for Litchfield Co., a resort development firm based in Pawleys Island, S.C. Houseman said land-use issues should be decided locally, and not by tax policy.

To others, however, the mortgage interest deduction for second homes is a fairness issue, particularly in light of the perennial federal budget deficit.

Barry Zigas of the National Low-Income Housing Coalition, for one, said he believes the current mortgage interest deduction system is inequitable. He said money being spent by the federal government on tax breaks for vacation homes for the affluent could be better spent helping house those who do not have first homes.

The questions surrounding the mortgage interest deduction for second homes could gain further currency if the number of people buying vacation homes leaps in the next few years, as predicted by the resort development industry's survey.

According to that survey, more than one-fifth of people under 39 years of age both expressed interest and said they had at least a 50-50 chance of purchasing recreational property, with people under 30 particularly keen on the idea. In contrast, 12.5 percent of those over 50 years old expressed the same sentiments, the survey found.

The National Association of Realtors, the International Foundation for Timesharing and the American Resort and Residential Development Association Political Education Fund paid for the study, which consisted of telephone interviews last spring with 5,636 people nationwide.

Its other findings included:

The highest rates of vacation-home ownership are among households that are headed by people ages 45 to 54.

About 1 in 13 U.S. households owns recreational property.

Time-share ownership of resort housing is increasing in popularity. Almost half of all new second-home owners since 1973 have been time-share buyers.

Florida is clearly the nation's second-home hot spot, with more people identifying it as the place where they own a vacation home, or would if they could.

While married couples make up only about 56 percent of all households, they make up more than 78 percent of all recreational property owners.

People who already own homes are far more likely to also own a vacation home. They are four times more likely to own recreational property than are apartment renters.

The median income nationwide of recreational property owners is $46,500, but among families earning $100,000 or more, nearly one-third own vacation homes.

On average, recreational properties are little-used: Total average usage came to only about 58 nights per year, or about eight weeks of annual use. About half that occupancy was by renters, with the owners, their relatives or friends using it for the equivalent of the other month.

More than half of the potential second-home purchasers said loss of the mortgage interest deduction would cause them to reconsider a vacation-home purchase, with 28.4 percent saying it would "greatly reduce" their interest and 30.4 percent saying it would "somewhat reduce" their interest. About 41.2 percent said loss of the mortgage interest deduction would have no effect on their decision to buy.