When you're looking for mortgage financing or refinancing alternatives on a home this fall, don't ignore what could be one of the best deals in the marketplace today: cut-rate, graduated-payment loans.

They're not for everybody, by any means. They have distinct risks and drawbacks that accompany their 11 and 12 percent rates. And they've been black sheep in the real estate field until recently: Many housing experts predicted that the public would never accept them.

But those experts were wrong. Graduated-payment, adjustable-rate loans are now the fastest-growing financing tool in the country. They accounted for nearly 25 percent of Merrill Lynch Realty's total home sales volume through August of this year in 300-plus offices in 27 states. That's $1 out of $4 in an estimated $6 billion in annual sales. Two years ago, they accounted for virtually none.

Graduated-payment and adjustable-rate loans represent 45 percent of the multi-billion-dollar volume this year of Fannie Mae (the Federal National Mortgage Association), the largest supplier of housing dollars in the country.

Like them or not, graduated-payment and adjustable-rate loans are a burgeoning force in the home market--and they are particularly attractive at a time of declining rates.

Here's how they work and why they're enticing consumers this fall:

Graduated-payment loans carry effective rates that are typically three to five percentage points below those prevailing on conventional, fixed-rate mortgages.

The payments increase -- often by $50 or $60 per month annually -- for periods of three to five years.

The effective loan rates are subsidized by the lender during the early years, and the home buyers are expected to pay back the "deferred interest" during later years.

A $67,000 graduated-payment loan to a town house buyer at 12.4 percent in this summer's 16 percent market, for example, would have carried a $701 first-year monthly payment. (The unsubsidized monthly payment would have been over $200 more. The 3 1/2 percent rate subsidy will be partially paid back through higher monthly payments during the next two years--$760 per month during 1983, $820 per month during 1984.

This fall's lower rates, however, allow the initial rate floor to be set much lower. Many homebuilders and some realty brokers using Fannie Mae and other graduated-payment plans can now offer rates below 12 percent.

For example, Colonial Mortgage Service Co. of Rockville is offering 95 percent mortgages (5 percent down payment) at 11 5/8 percent with 2 1/2 points up front from the borrower. (A point is 1 percent of the mortgage amount, payable at or before settlement.)

The monthly payments rise over a period of five years by a maximum of 7 1/2 percent a year. Then the loan rate and monthly payment are readjusted to account for interest rate movements that occured during the course of the loan term.

Shearson-American Express Mortgage Co. of Springfield is offering 10 7/8 percent graduated payment loans loans up to $107,000 with 5 percent down. Shearson wants five points up front for its loans.

The recent interest rate declines have not only cut the initial rates on graduated payment mortgages, though. The base rate against which the loan-payments are calculated has now dropped to 13 3/4 percent and 14 1/2 percent -- down from 16 percent and higher. The size of the deferred interest payment to be recouped later, in other words, will be smaller, and payment increases will also be smaller from year to year.

Perhaps most important to buyers who've been frozen out of the market, the 10 and 11 percent starting rates represent the first real opportunities in two years to qualify for a loan of any type.

Every percentage point decrease in conventional market rates allows an estimated one million buyers to qualify for new home loans, according to national housing economists. Graduated-payment plans expand the pool of qualified buyers by an additional three to six million people. And when builders add on "buy-downs" -- their own all-cash rate subsidies to cut monthly payments -- the effective rates on many new home loans can go as low as 9 percent.

All of this comes with a price, of course.

Graduated-payment loans are essentially adjustable-rate mortgages when you strip them down. They are tied to national cost-of-money indexes that are unpredictable and uncontrollable.

If rates rise sharply during the first three to five years of your 10 to 11 percent loan, for instance, they won't affect your out-of-pocket payments until 1985 or 1987. But then, you could be hit with payments computed on a 17 to 18 percent loan, plus a larger principal amount than you started with.

You'll have to repay those years of subsidies, in other words, at a higher price than you originally figured. (And perhaps at a rate higher than you could afford at the time.) That's the inherent risk with graduated-payment plans.

But if you think getting into a house at a low rate is worth the risk -- and if you believe rates will remain at moderate levels or drop during the coming several years -- the graduated-payment boom of 1982 may be right for you.

Check it out.