SAN FRANCISCO — Erica Jostedt loves to shop, but she hates paying with cash or a check. There's rarely more than $20 in her wallet, and she doesn't carry around her checkbook because she usually needs it just once a month to cover the rent at her San Francisco apartment.

"I get so annoyed when I go into a place that only takes cash that usually I end up going somewhere else," she said.

Jostedt, 24, was born in the 1980s, the leading edge of a generation that is shunning paper payments like no other before it.

These young consumers so consistently reach for debit and credit cards that Visa USA has anointed the age group "Generation Plastic," or "Gen P."

Their habits are driving even more merchants to accept debit and credit cards, fueling legal battles over the fees and raising more concerns about the nation's shriveling savings rate.

Plastic payments — including online commerce — now account for 50.4 percent of the spending among consumers ranging from 18 to 24 years old, with cash and checks making up 41.1 percent of their spending. Consumers 25 to 34 years old spend about 45 percent either way, while everyone older still uses cash and checks at least half the time, according to Visa, the nation's largest payment network.

"All paper-based payments are in retreat," said David Robertson, publisher of the Nilson Report, a newsletter that's been following spending trends since 1970. "People of a certain age don't even know where their checkbook is."

Judy Jostedt, Erica's 55-year-old mother, isn't so sure that's good. Although she uses debit cards more frequently, Judy still writes about a dozen checks each month, partly because she feels her canceled checks help her monitor spending. "I worry that kids today don't even know where all their money is going every month," Judy said.

As a whole, Gen P isn't using credit cards any more frequently than other age groups, but depends more heavily on debit cards. Gen P uses debit cards to pay for 28.2 percent of purchases compared to just 7.1 percent among those older than 45, according to Visa.

Debit cards — which avoid debt by withdrawing the purchase amount from a consumer's bank account — were used to pay for an estimated 23.1 billion transactions nationwide during 2005, surpassing the estimated 20.3 billion transactions paid by credit card, according to the Nilson Report.

But consumers tend to spend more with credit cards, which paid for an estimated $1.75 trillion in purchases during 2005 compared to an estimated $872 billion on debit cards, the Nilson Report estimated.

Even though they aren't directly adding to consumer debt, debit cards are diminishing the nation's already paltry savings rate, said Howard Dvorkin, president of Consolidated Credit Counseling Services. That's because consumers paying with a plastic card tend to spend substantially more than someone paying with cash or check, Dvorkin said.

So even if they aren't increasing their debt by buying with a credit card, consumers who use debit cards might wind up with less money to save than they would if they paid for things with cash.

"There's no pain involved when you pay with plastic," Dvorkin said. "But there is some pain when you go out and you have to part with cash. You worked hard for that green stuff, and you aren't as apt to spend it."