When Yana Yanovsky of Huntington Beach bought her high school homecoming dress last year, she didn't have the $80 in cash. So it went on her parents' credit card.

This year, things were different. As a senior at Edison High, she got her own card. It was easy, she said. One of the nation's largest banks sent her a letter inviting her to apply.

These days, giants Chase Manhattan Bank, Citicorp and other credit card issuers are competing to sign up high school students. They are targeting college-bound seniors, regardless of income, offering them Visa or MasterCard accounts in their own names. The cards have a $500 limit but no security deposit. The only caveats: Students must have no credit problems, and parents must co-sign for minors and ultimately are responsible for the bill.

The reason for the move is clear. The traditional credit market is saturated, with more than 255 million Visas and MasterCards in circulation. So, banks are thinking younger, hoping to gain new customers now and build long-term relationships for the future.

"What issuers discovered is that if you get your hooks into a consumer early, there's a loyalty that springs from that," said industry analyst Bob McKinley of RAM Research Corp. in Maryland. "They'll stay with the credit card company for 10, maybe 15 years."

The highly competitive credit industry is tight-lipped about details of its high school recruiting efforts. Some banks say they have been test marketing to teen-agers for years, but industry analysts say this is a major campaign that began this past school year.

Banks tried to go younger once before. A decade ago, the industry saw that the market was saturated and decided to sign up not just those who had solid incomes, but those \o7 likely\f7 to have solid incomes.

That meant college students. Competition for their accounts became so intense that banks set up card tables at class registration lines and slipped applications under dormitory doors. But even that market is filling up, so attention has shifted to college-bound seniors.

It is too early to tell how teen-agers and plastic will mix. So far, the track record is based mostly on students who use their parents' cards. (MasterCard International estimates that 4% of high school students have their own and another 24% use their parents'.)

Most card usage seems to occur in affluent areas. A spokesman for the Wherehouse music and video chain said that in high-income areas up to 15% of teen-agers' purchases are on credit.