Faced with sobering conditions, companies that issue MasterCard, Visa and other cards are rushing to stanch the bleeding, even as options once easily tapped by borrowers to pay off credit card obligations, like home equity lines or the ability to transfer balances to a new card, dry up.

Big lenders  like American Express, Bank of America, Citigroup and even the retailer Target  have begun tightening standards for applicants and are culling their portfolios of the riskiest customers. Capital One, another big issuer, for example, has aggressively shut down inactive accounts and reduced customer credit lines by 4.5 percent in the second quarter from the previous period, according to regulatory filings.

Lenders are shunning consumers already in debt and cutting credit limits for existing cardholders, especially those who live in areas ravaged by the housing crisis or who work in troubled industries. In some cases, lenders are even reining in credit lines after monitoring cardholders who shop at the same stores as other risky borrowers or who have mortgages from certain companies.

While such changes protect lenders, some can come back to haunt consumers. The result can be a lower credit score, which forces a borrower to pay higher interest rates and makes it harder to obtain loans. A reduced line of credit can also make it harder for consumers to manage their budgets, because lenders have 30 days to notify their customers, and they often wait to do so after taking action.

The depth of the financial crisis has shocked a credit-hooked nation into rethinking its habits. Many families once content to buy now and pay later are eager to trim their reliance on credit cards. The Treasury Department, which is spending billions of dollars in taxpayer money to clean up an economic mess brought on in part by all sorts of easy credit, recently started an advertising campaign inviting consumers to check into the “Bad Credit Hotel,” an online game that teaches the basics of maintaining good credit.