For many credit card holders, there has never been a better time to owe money. Two years of interest-rate reductions have decreased the average interest rate charged by credit cards to 14.3%, the lowest point in the industry's 35-year history.

By comparison, the average rate for Visa, MasterCard, American Express and Discover cards one decade ago was 18.23%, according to the

Nilson Report

, which covers the credit card industry.

But while the

Federal Reserve's most recent rate cuts have dropped short-term borrowing costs for credit card companies, a substantial number of credit card holders haven't seen the benefits.

That's because about a quarter of all holders have cards with fixed rates that don't respond to reductions in interest rates. In addition, a minority of those who pay variable rates have cards with "floors" below which rates are not allowed to fall. The rate floor for consumers is based on the prime rate -- the interest rate banks charge their most creditworthy customers, currently 6.75% -- plus another 5 to 7 percentage points. Customers with weaker credit histories pay at the higher end of the scale.

"Typically, the floor for most credit card companies was hit about three Fed rate cuts ago," says Matt Coffin, CEO of LowerMyBills.com. "So even if the

Fed rate were to go to half a percent, they will not lower their rates any lower."

How to Lower Your Credit Card Bills

That's bad news for many debt-laden cardholders. According to the

Nilson Report

, the average bankcard debt per cardholder is a hefty $4,483. Fortunately, plenty of card companies offer excellent promotional deals for new customers.

But first, people should check the rates on their monthly bills every three months to make sure they know exactly how much they're paying, Coffin recommends. "Credit card companies are constantly looking at the percentage of defaults, they're tightening or loosening credit,

and they're looking at what the Fed rate is doing. So the rates are in flux constantly."

Once cardholders know their rates, they may find they can save money by signing up with a new company and transferring their balance to a card with a lower rate. (Card companies typically don't allow consumers to transfer their balances from an existing card to another card within the same company.)

Customers who carry balances "are probably best served by surfing the balance transfer rates from various companies, taking advantage of teaser offers and being scrupulous about moving balances as higher rates kick in," says David Robertson, president of the

Nilson Report

.

The best cards typically offer short-term promotional rates that last from a few months to a year, say those familiar with card offers. Such experts also advise consumers to stick to no-fee credit cards.

Consumers who manage to get a great promotional rate should be aware that it's often contingent on prompt payment of their bills. Coffin of LowerMyBills.com cites the example of a Citibank card with a rate that jumped from a low, promotional 12.9% to a steep 24.9% because the payment was a few days late.

More Bill-Lowering Tips

Consumers should be aware that cards that tout extra benefits often don't provide competitive rates. Store credit cards tend to charge the highest rates of interest, though they may try to sweeten the deal with benefits like airline miles that accrue with in-store purchases, Coffin says. Especially amid the current economic uncertainty, "people need to be paying less on all their bills and stay away from hokey benefits," he says.

Finally, consumers can try to negotiate with their credit card company for a lower rate. Most likely that will work for those who can claim legitimate financial distress, whether it's from a job loss or lengthy illness. In the worst-case scenario, when even a reduction in rates wouldn't help much, customers who have suffered a dramatic loss of income may be able to restructure their debt payments.