If you're in the same position as most consumer borrowers, financial advisers say, you should be aware that time is not on your side.

In the late 1970s and early 1980s, there was a real incentive to borrow heavily. Since inflation was running at a rapid rate, you paid off loans with cheaper and cheaper dollars as time passed.And every nickel of interest you paid was deductible on your tax return, no matter what you used the money for.

But those days are long gone. Interest rates, though they may be nominally lower now than they were several years ago, are actually very high in comparison to today's inflation rate.

And the deduction for consumer interest - on credit-card purchases, auto loans and so forth - is fast disappearing.

Under the Tax Reform Act of 1986, just 40 percent of consumer interest will be deductible on 1988 tax returns.

The percentage drops to 20 in 1989, to 10 in 1990, and to zero thereafter.

"If you have not already done so, you should consider repaying existing personal debts as soon as possible to avoid additional non-deductible interest expense," the accounting firm of KPMG Peat Marwick says in a booklet on 1988 yearend tax planning.

That goes especially for credit-card debt, analysts say.

In some areas of the country, competition between lenders has pushed interest rates on outstanding credit-card balances down from their former levels. But according to the organization Bank Card Holders of America, the average rate still stands at 18.3 percent.

If you have some money you want to invest for an assured high return, suggests the financial advisory Donoghue's Money Letter, what better use for it than to pay off credit card debt?

"We dare you to find another 18.3 percent sure thing today," the newsletter says. "It just doesn't make sense to pay this kind of interest."

A special problem can arise with a car loan, adds Jerry Karbon of the Credit Union National Association, a trade group in Madison, Wis.

Since many cars are bought today with loans extending over five, six or even seven years, their owners often face an unpleasant surprise when they prepare to trade them in for new models.

The car's value has depreciated as fast as, or faster than, the loan balance has been reduced, so that the vehicle has no effective trade-in value.

"Paying for the car over a longer period reduces the monthly payment, but it repays the loan so slowly that it may take three years or more before there is any positive equity in the vehicle," Karbon says.