NEW YORK — Not paying attention to your credit score can cost you a lot of money.

Many people don't know that their score — a three-digit number derived from an analysis of how they handle debt — is the key determinant of what interest rate they'll pay on credit cards, auto loans and home mortgages. The lower a person's score is, the higher the interest rate and, therefore, the higher the cost for the loan.

A new study by the Consumer Federation of America and Washington Mutual Inc., the Seattle-based savings bank, found that fewer than six out of 10 Americans have obtained their credit scores, and half of those surveyed consider their understanding of the scores as "fair" or "poor."

Stephen Brobeck, executive director of the nonprofit CFA, which is based in Washington, D.C., said he found the statistics disturbing because consumers can't work to improve their scores if they don't know what the scores are.

"Many people don't understand what the score represents and what a good score is," he said. It's important, he added, "because the role credit plays in people's lives is huge."

RANGE OF SCORES

The credit score most people encounter is a FICO score, which is named for the Minneapolis-based Fair Isaac Corp. that created it.

FICO scores range from 300 to 850. Scores of 700 and above are considered good. About half of consumers fall into this category.

Those below 600 are weak, and some 15 percent of Americans fall into this range. The rest are in between.

Fair Isaac gives this illustration of how different scores can affect consumers: A borrower with a score of 700-759 could qualify for a 30-year fixed-rate mortgage loan with a 6.6 percent interest rate requiring a monthly payment of $1,916. A person with a score of 620-659 would get a 7.7 percent rate on such a mortgage and have to pay $2,138 a month.

There are ways for consumers to improve their scores — most importantly by paying bills on time and not maxing out credit cards — but first they need to find out what their scores are, and there are several ways to do that.

The scores are generated off reports compiled by the three main major credit reporting agencies — Equifax, Experian and TransUnion.

Since 2005, consumers have been entitled to a free copy of their report from each agency once a year. Reports can be requested at the Web site www.annualcreditreport.com or at the toll-free number 877-322-8228.

While the credit reports are free, consumers must pay for credit scores — generally at a cost of $10 to $15 — from the credit agencies.

There's a link to each of the agencies from the annual report Web site, or consumers can go directly to the agency sites at www.transunion.com, www.experian.com or www.equifax.com. Fair Isaac also sells scores at its consumer site, www.myFICO.com.

LENDERS CHECK

Lenders, including mortgage brokers and banks that write auto loans, pull credit scores when they're working to pre-approve a consumer for a loan, and many of the lenders will share the score with the borrowers. There's generally no charge to the consumer.

The credit agencies are developing an alternative to the FICO score, known as the VantageScore, which is in the process of being rolled out to lenders.

VantageScores range from 501 to 990 and are assigned letters like an academic scale. So scores of 501 to 600 rate an "F" while 901-990 get an "A."

Consumers who find that their scores are low can take a number of steps to improve them, said Andy Jolis, head of www.myFICO.com.

The two most important factors in determining a score are payment history and how much of your available credit you're using.

"That means that paying on time and keeping your balances low are things you need to focus on to improve your score," Jolis said.

The score also takes into account how long you've been a borrower, how much new credit you've applied for and miscellaneous factors, such as the mix of loans a consumer has.

That means, for example, that consumers shouldn't be applying for a whole bunch of retail store cards at the same time they're seeking a mortgage because the flurry of applications could reduce their score.

Barrett Burns, the chief executive of VantageScore, said Experian and TransUnion have begun making Vantage-Scores available to consumers.

He said utilization of credit was something lenders watched closely.

"Say you've got a line of credit of $100,000 and you're using 80 percent of that," he said. "A lender will look at that and think you don't have much room for error because you don't have a lot of liquidity left."

So a consumer who holds the use of that line to $30,000 to $50,000 will merit a better score, Burns said.

Consumers looking to close down some of their credit cards should consider the impact on their total available credit.

"It's a mistake just to go out there and reduce the number of cards if the result is to increase the utilization rate," Burns said.

Burns said consumers also should think carefully before canceling their oldest cards in favor of newer ones because the score "reflects how you've handled debt over time."