The degree of consumer protection you get on your next adjustable-rate mortgage could depend heavily on where you live or where you're moving -- in addition to how hard you bargained with the lender.

That's one of the conclusions from a new, national statistical profile of adjustable-rate loans conducted by the U.S. League of Savings Institutions. Based on samples of mortgages made at 1,100 savings and loan associations and savings banks across the country, the study turns up striking differences in adjustable-rate-mortgage shapes, forms and customs from city to city.

Home buyers in the large New York-northern New Jersey metropolitan area might be intrigued to know they live in the only major market in the national sample where rate adjustments by lenders are tied to highly volatile six-month Treasury bills. Almost 91 percent of the adjustable mortgages closed by S&Ls and savings banks in that market carry the six-month-rate-change feature.

Adjustable-rate-mortgage borrowers at S&Ls and savings banks in cities such as Washington, Milwaukee and Boston, by contrast, are likely to be offered rates tied to one-year Treasury bills.

What does that mean for borrowers in these far-flung cities? Home buyers in the New York-northern New Jersey area are relatively more exposed to changes in the economic weather -- good or bad -- than are typical buyers of adjustable-rate mortgages in other major metropolitan areas.

If interest rates jump four points in six months and a mortgage is indexed to six-month Treasuries, the borrower's base rate will reflect that increase. On the other hand, if rates drop four points, the borrower whose loan is tied to the short-term index will benefit faster than a buyer whose loan is tied to a longer index.

Other key adjustable-rate features that differ sharply from market to market are the types and sizes of lender "caps" on potential rate and payment increases, according to the new statistical data.

Caps function as fail-safe devices to protect the borrower in the face of unexpected, severe changes in interest rates. Generally speaking, the lower the cap, the greater the protection for the borrower (and the less protection for the lender). The higher or looser the caps, on the other hand, the greater the risk of future rate or payment shock for the buyer.

Caps take three basic shapes:

*Lifetime limits on the mortgage rate, beyond which the loan cannot go, no matter what's happening in the economy.

*Annual rate-increase limits.

*Annual payment-increase limits.

Home buyers in many markets get little or nothing in the way of annual mortgage-payment increase caps, according to the survey data. Borrowers at thrift institutions in St. Louis, Philadelphia, Milwaukee, Cincinnati and Boston stand more exposed to year-to-year payment increases than do borrowers in, say, Washington, Los Angeles or metropolitan New York, where annual payment caps are common.

Lifetime rate caps are more standard features nationwide, the study found, but even here the city-to-city differences can be important.

Although the average life-of-the-loan cap across the country averages between 4 and 5 percentage points (i.e., the rate on your 12 percent loan will never rise beyond 16 or 17 percent), lenders in some areas routinely offer caps lower than 3 percentage points or higher than 5 percentage points, or none whatsoever. Roughly 90 percent of the adjustables in metropolitan New York, for instance, come with life-of-the-loan caps of 4 percentage points or less (a definite plus for the consumer).

Contrast that with Milwaukee and Philadelphia, where roughly one-third of the adjustables surveyed offered no lifetime caps at all.

Understanding the range of consumer-protection features available in adjustables -- and what they cost versus their benefits -- is probably one of the toughest tasks facing mortgage borrowers in this fall's housing marketplace.

A free guide to help borrowers through the maze has just been published by the Mortgage Bankers Association of America. For a copy of "ARMS," write to the Mortgage Bankers Association, 1125 15th St. NW, Washington, D.C. 20005.