Gail Cincotta, the Chicago housewife who led a national crusade to make home loans available in city neighborhoods, calls them "the new arm-and-leg mortgages."

Richard T. Pratt, the federal official who helped create them, hails their arrival as a pathway to "a healthy, viable housing finance sector."

Both are referring to the new adjustable-rate home mortgage loans.

Although opinions differ about their desirability, experts predict that "adjustables" will change profoundly the way Americans pay for housing. Some even say their arrival signals an end to the nation's golden age of homeownership -- a shutdown of the mechanism by which so many Americans reach, and remain in, the middle class.

Adjustable mortgages burst onto the real estate market last month with a ruling by the Federal Home Loan Bank Board, the agency which regulates the nation's savings and loan industry. The board, chaired by Pratt, ruled that savings and loans institutions may issue mortgages with rates of interest that rise or fall without limit over the duration of the loan. This allows lenders to "hitch" mortgage rates to some changing indicator of prevailing interest rates, such as that paid by Treasury bills.

Beyond that, the board provided little direction about the form these mortgages must take, leaving the details to be worked out between lenders and borrowers. S&Ls now are devising terms for the new mortgage and are expected to begin marketing them in a few weeks.

Lenders say conventional mortgages -- in which the interest rate and monthly payment stay the same over the life of the loan -- still will be offered. But "conventionals" will likely carry higher interest rates than newly issued adjustables, lenders say, because S&Ls will want to protect themselves against future increases in rates paid depositors.

Initial publicity about the new loans has centered on the consumer protection aspect: Will buying a home suddenly become a high-stakes gamble in which the buyer can "lose the ranch" if interest rates shoot past his ability to pay?

That question quickly leads to larger questions about the fading chances for homeownership among young families and what that portends for urban areas.

Cincotta, who now heads a neighborhood lobbying effort called National Peoples Action, argues that the arrival of adjustable-rate mortgages underscores "the biggest neighborhood issue of the '80s -- high interest rates and a lack of money for housing."

Ten years ago, she explained, the problem facing city neighborhoods was redlining -- keeping home purchase and fix-up loans from going to residents of supposedly high-risk urban areas. Today both the inner city and the wealthier suburbs are starving for affordable mortgages.

Interest rates have climbed beyond the point where most home shoppers can afford to take out a loan.

For example, a Chicago-area home buyer who signs a 29-year, $60,000 mortgage at the current rate of 17 1/4 percent can look forward to monthly payments of $868.55 and a payout over the life of the mortgage of $302,255.

Family finance counselors have long advised buyers to limit their monthly housing payment (including mortgage, taxes, insurance and utilities) to one-fourth of their income. Under that formula, fewer than 5 percent of American households -- those making over $50,000 a year -- would be deemed able to safely undertake such a home purchase.

If this were a temporary phenomenon, a jag on an economist's line graph, buyers could wait until rates come down. Many indeed are waiting. But they may find themselves waiting forever, Cincotta warns, because high interest rates on mortgages are fast becoming a de facto national policy.

"The new policy is to cut off money that has gone to home equity," she claimed, "and redirect our savings toward industrial growth."

Cincotta concedes that federal officeholders haven't announced such a policy officially, but she points to a string of recent articles and speeches by Washington economists, both in and out of government. Their general thrusts is that America has become "over-housed," that cheap mortgages have drained off money that should be lent to businesses for modernizing the nation's industrial plant.

A leading proponent of this theory is Anthony Downs, senior fellow at the Brookings Institution, a Washington think tank.

Downs recently has argued that fixed-rate mortgages, often carrying interest rates made cheaper by federal mortgage insurance, have combined with favorable income tax laws to tempt Americans to overspend on housing.

Cincotta dismisses this theory as elitist. "Downs may be talking about where he lives," she said. "But where I live we don't have enough homeownership. And that's still the key to anchoring my or any other neighborhood.

"High interest rates amount to redlining by class," she added. "We're cutting more and more people out of owning a home. The government is fighting inflation with high interest rates, but the cure is killing the housing industry, and it's dying from the bottom up."

Defenders of adjustable rates, however, make a strong case that the S&Ls had no choice but to force home buyers to pay the same high rates as anyone else. As interest rates climbed into double digits late in the 1970s, they explain, savers abandoned 5 1/4 percent savings accounts for higher-yielding Treasury notes and money market funds.

When the S&Ls won federal permission in 1978 to match the interest paid by Treasury bills, the savings outflow was stemmed partially, but many lenders with loan portfolios full of long-term, low-interest mortgages still are losing money.

"What we're seeing is a revolt of the small saver," said an S&L executive, "and the victim of the revolt has been the small borrower."

Cincotta counters that the federal government cannot remain on the sidelines and blames "market forces" for the dearth of home loans.

"The first thing we need is a full congressional investigation of the new adjustable mortgages," she said. "We need some protection for the borrower. Now there is none."

Above all, Cincotta wants Washington to revive homeownership as a goal of national fiscal policy.

"If that doesn't happen," she said, "the only way my children will own a house is to inherit mine. And I have six kids."