GRASS VALLEY, CALIF. -- Two months ago, Jack Parman stepped outside his modest frame home on a Sierra Nevada hillside for a breath of fresh air.

What should have been an interlude of pure pleasure in this idyllic, tree-lined setting turned instead into a moment of dismay: The early morning calm he had savored since moving here in 1940 was gone, replaced by the dull, incessant roar of rush-hour traffic.

"It was just like staying all night in a hotel in San Francisco," Parman said. "I realized then that this area has been destroyed. It's just another city now."

In just 20 years, Grass Valley and neighboring Nevada City have been transformed from quaint mountain villages into trendy, high-growth cities by America's increasingly mobile and affluent older population.

The once-sleepy Gold Rush communities -- and other pristine, picturesque rural areas across the country -- have emerged as the primary destinations for retirees seeking to escape the congestion, crime and pollution of big cities.

From Pennsylvania's Pocono Mountains to Michigan's Upper Peninsula, from California's Gold Rush country to East Texas's Piney Woods, senior citizens increasingly are forgoing traditional retirement areas in favor of regions where they vacationed during their working lives.

Demographers and sociologists have identified 500 "retirement" counties across the United States -- many just beyond the metropolitan suburbs -- where growth in the 1980s was triple the average in rural counties and nearly double the growth in urban areas. The list includes 78 Texas counties.

"This retirement migration phenomenon is relatively recent," said Nina Glasgow, senior research associate at Cornell University's Department of Rural Sociology. "There is a greater affluence among older people in general, and this has fueled this trend."

The little-noticed but unmistakable migration of retirees from metropolitan to rural areas is expected to help reshape American life well into the 21st century:

The flood of senior citizens is bringing demand for new, sometimes different, businesses. In one Texas community, businesses are responding to this new market by offering a club and newsletter for senior citizens only.

The migration of the elderly is creating new service jobs, which in turn attract more working-aged Americans.

In many instances, the population surge has fueled a serious conflict between longtime residents and newcomers.

In some communities, residents complain that the influx has led to unbridled and poorly planned growth that threatens to destroy some of the nation's most unspoiled areas.

Property values are skyrocketing in some boom areas, driving affordable housing beyond the reach of all but the most affluent.

The growth has strained transportation, water and sewage systems to the limit, forcing some communities to consider tax increases or impose higher fees on construction.

For some people in areas such as Grass Valley and Nevada City, about an hour northeast of Sacramento, paradise was discovered -- only to be lost almost as quickly.

"It's like trying to put too many people in a bottle," said one Nevada County resident, who is leaving only 10 years after designing and building his dream home.

"The quality of life has gone {downhill} around here, and I don't see any possible solutions," said the former San Francisco Bay Area executive, who requested anonymity for fear that his comments could affect the sale of his mountainside residence.

"It's nonsensical. It's going to take another five or 10 years, and then it's going to be a crisis. I don't want to be involved in it," he said.

According to Glasgow, the metro-to-rural migration by retirees has been spurred primarily by a rosier financial picture for the nation's elderly: improved Social Security benefits, increased personal savings and investments, and more private pension plans.

Americans also are staying healthier longer and living longer -- and the over-65 population is ballooning.

In the 1980 census, there were more than 5.3 million people 65 years or older in the United States. The government estimates that that number will be more than 31 million in 1990 and more than 34 million in the year 2000. That trend will continue in the early years of the 21st century as the baby boomers age.

Experts say that most retirees don't move after leaving the work force. But those who do tend to remain in the region where they built their careers.

"They don't have to go to a strange region," said Calvin Beale, a senior demographer for the Agriculture Department who identified the 500 gentrifying counties. "It's one they're comfortable with, and they may already have had a second place there anyway."

Nowhere is the familiarity theory more evident than in California's Gold Rush country, where retirees from nearby urban areas are moving.

"You're not moving miles from everything you know," said Loraine Roberts, 63, of Nevada County, who retired here from the San Francisco Bay Area in 1982 with her husband, Harold, 65.

Nevada County's population has more than tripled since 1970, from 26,500 to an estimated 81,400 or more today. Although demographers won't speculate on the population of senior citizens until they see the 1990 census data, they attribute much of the growth to retirees.

Experts say the median age of Nevada County residents was 38 in 1970. By 2020 it is expected to climb to 44.

In the 11 counties of the Gold Rush country -- where dreams of riches prompted an invasion of prospectors 150 years ago -- today's newcomers find a lifestyle vastly improved over that of California's big cities, with less congestion, pollution and crime. Many also find themselves better off economically.

The luckiest retirees are taking advantage of skyrocketing property values in the San Francisco Bay Area or Los Angeles to turn a $30,000 residential investment 30 years ago into a $500,000-plus sales price in the 1980s. With construction costs in the Sierra Nevada still lower than in major metropolitan areas, many elderly people found they could build a house and have money left to live on.

But this fulfillment of the American dream is creating nightmares.

The demand for homes in this mountain oasis is driving property values beyond the reach of all but the most affluent.

On Banner Mountain, 3 1/2-acre lots in a new subdivision are selling for about $190,000 each. Fees to reduce the strain on the water, sewer, transportation and school systems add thousands of dollars to the cost of every house.

Real estate brokers report that the cost of land and housing is climbing by 2 percent each month. By mid-April, the median home price in Nevada County was $165,000 -- up from $149,900 in February.

Indeed, there already are indications that the typical working-class person has been priced out of the market.

Last year, when wildfires swept the drought-stricken county, many families were found living in shacks or other makeshift housing that had not been approved by government inspectors and did not meet basic safety and health codes.

And the morning rush hour sees a considerable amount of traffic bound from the Sacramento suburbs for Grass Valley and Nevada City -- presumably service workers who cannot afford to live in Nevada County on service-industry wages.

The explosive growth also has caused political convulsions as newcomers and longtime residents square off over the county's development. Nevada County locals say that in the past decade there has not been a city council or county board of supervisors that has not been recalled en masse or faced a recall attempt.

Longtime county residents, used to the vagaries and peculiarities of small-town politics, resent the activism of newcomers. In turn, newcomers complain that longtime residents want to see the growth continue because it has pumped up business profits and property values.

Everyone agrees that it is the newcomers who most zealously want to halt growth and maintain the rural environment.

"The one thing you can say is, once people are in here, they've got theirs, and they don't want any more" growth, said Dave Mirtoni of the Placer County Community Development Department. "They want it to maintain its rural character."

Pat Norman, Nevada County senior planner, said newcomers had reshaped the political scene by becoming involved in zoning issues and development proposals.

"There is a fairly high percentage of people who fit the category of being retired. They didn't move up here because they're poor. They're sophisticated, articulate, educated and they didn't retire real old," Norman said. "They've got time on their hands, and they're concerned about land-use decisions that might affect their quality of life."

Both longtime residents and newcomers say the political divisions are so deep that local governments can't reach a consensus on waste disposal, water and other problems.

The intense growing pains experienced in Nevada County are not unusual in America's gentrifying counties, according to sociologists and demographers.

Not all areas are realizing such a dramatic growth in population and escalating property values. But many of the social, political and environmental strains are the same.

In Henderson County, Tex., longtime residents and the so-called Lake People -- retirees living near the county's reservoirs -- often find themselves at odds over county services. Population in the county, southeast of Dallas, jumped more than 30 percent between 1980 and 1988.

"You have this line of resentment between old-timers and the Lake People," said County Judge Winston Reagan, who is retiring after 24 years. "The Lake People refer to themselves as the stepchildren or the 'lake trash.' "

He said some newcomers, especially those from major cities such as Dallas, have trouble accepting the lower level of public services in rural areas.

Still, the influx of retirees has helped Henderson County weather the worst effects of the oil bust and economic downturn that hammered much of Texas, according to Reagan and others.

The building boom has increased the county's tax base substantially. Many businesses in Athens have tailored their marketing for the newcomers. They have established a "Double Nickel Club" for residents age 55 and over, mailing a monthly newsletter to about 20,000 residents that details discounts and specials for senior citizens.

Ken Davis, executive vice president of the Athens Chamber of Commerce, said his group answers about "four or five" inquiries each day from potential residents or visitors.

"You just treat them like any industrial prospect," he said. "If they come here, they'll spend money."

In Grass Valley, some longtime residents recognize that economic fact of life. The realization gives them mixed emotions about the growth in the California Sierra.

Former Nevada County Commissioner Bob Wilder, his voice occasionally breaking, related how skyrocketing property values and resulting tax considerations have forced him to subdivide much of the family's beautiful meadowlands near Grass Valley.

Yet, he said, the growth has led to construction of a state-of-the-art medical center and rapid improvement of the local school system -- something that will benefit his grandchildren.

"Our type of lifestyle has changed," Wilder said. "I don't think it's worse, it's just different."

Betty Simpson, a neighborhood activist who moved from Sacramento to Nevada County in 1978, said she hopes the growth can be slowed at least temporarily. That way, she said, planners can draft a blueprint for managing the growth and maintaining the area's special character.

In the meantime, though, she and her husband have considered moving because the growth has hurt their quality of life.

"You get kind of a doomsday attitude from time to time," she said. "Maybe its very attractiveness is what doomed it."