If you're making any major purchases on credit, you should soon start finding lower interest rates at banks, savings and loan associations and credit unions.

Interest rates are falling throughout the economy, due to the severity of the recession and to the easier-money course now coming out of Washington. Many institutions have reduced their charges, not only on business loans, but also on mortgages and consumer loans.

You cannot, however, take these new rates at their face value. What really matters is the "real" interest rate -- the difference between the given rate and inflation.

Last year, conventional mortgages ran at 15 percent and inflation at 10 1/2 percent. Assuming that your earnings rose with the inflation rate, the real burden of that mortgage on your 1981 standard of living was only 4 1/2 percent.

Now, mortgage rates are around 13 to 15 percent, with inflation running at 5 percent. That means you are paying 8 to 10 percent in "real" interest for your housing loan.

So if you think that today's falling interest rates still feel high, you're right. Even if your 1982 wage increase matches the inflation rate, it will be harder for you to carry a new mortgage this year than it was in 1981.

People who took adjustable-rate mortgages at high rates last year should soon be getting some relief. On an adjustable mortgage, your interest rate -- hence your monthly payment -- rises and falls with the general level of rates or with your institution's cost of funds. At banks and S&Ls around the country, adjustable mortgage rates are now heading down, sometimes by 1 percent or more. If you borrowed at 17 or 18 percent, your monthly payments should soon be adjusted downward.

Some institutions adjust their mortgage rates with a lag, in which case your payments may not fall for a couple of months.

If you took a fixed-rate mortgage at 17 percent, your monthly payments will remain the same. You might talk to your bank or S&L, however, about renegotiating at a lower rate. No one knows how much lower mortgage rates are apt to go. If the economy stays soft and Washington hews to its easier-money line, rates still have a way to drop.

If you're taking a new mortgage and have a choice between fixed or adjustable rates, you face the following considerations: Fixed-rate mortgages usually cost a little more, but they guarantee your present monthly payments even if interest rates should rise again. Adjustable mortgages, by contrast, usually cost less at the beginning and also promise lower payments when interest rates fall. But they also require higher payments if rates go back up.

Many people like fixed-rate mortgages. They protect you against the possibility of higher payments, and you can always refinance at lower rates if borrowing costs continue to decline. But given the possibility of prepayment penalities and a second round of closing costs at refinancing, rates usually have to fall decisively to make refinancing worthwhile.

Sometimes your bank or S&L will knock a point or so off your mortgage rate during an interest-rate decline without going through the expense of a new closing. But you have to ask.

Auto loans are down a couple of percentage points at many institutions, as are the rates on consumer loans. Rates vary widely from one institution to another, but you should also be able to find new-car loans in the 14-to-15 percent range and unsecured personal loans at 16 to 17 percent.

Some car dealers are financing autos at around 12 percent. But to get that low rate, you'll usually find yourself paying more for the car than would otherwise be the case, or getting less for your trade-in.

Most retail credit and bank-card loans remain unchanged at around 18 to 23 percent. After 5 percent inflation, the real burden of these loans on your standard of living is now 13 to 18 percent, a heavier real price than you paid a couple of years ago.