If your credit cards haven't suffered meltdown during the holidays, there's more "plastic cash" in store. Just arrived or coming soon: phone calls, fast food, movies, groceries, even parking tickets on credit.

Improvements in technology, consumer demand for convenience and a search for new markets in a society approaching credit card saturation have combined to send the major credit card companies into previously uncharted waters."It's a move toward the 'smart card' that banks have been talking about for decades," says Gerri Detweiller, spokeswoman for the consumer group Bankcard Holders of America.

The latest offering on a nationwide basis by the three largest credit card companies - American Express, Visa U.S.A. Inc. and MasterCard International Inc. - is long-distance phone billing.

Earlier this year, Visa, in conjunction with MCI Communications Corp, launched VisaPhone, a service that allows card holders to use their credit cards as a long-distance calling card.

In October, American Express introduced its Connect Plus program with MCI and US Sprint, and in November MasterCard followed with its MasterPhone, also utilizing an agreement with MCI.

AT&T is also promoting its own Universal Card, a Visa or MasterCard and calling card in one.

In each of these systems, bills are paid through the credit card account.

Detweiller said some of the plans offer savings on long-distance calls, but she warns that card holders who fail to pay their bills in full each month could instead raise their phone bills through the hefty interest rates charged by some banks issuing Visas and MasterCards.

But the credit card companies say the convenience of eliminating the need for a calling card is a major attraction.

"For Visa members' banks, the market is quite large and for consumers the convenience is quite obvious," said Visa spokesman Gregory Holmes.

While the average American carries eight different credit cards, according to one survey, a Visa report on the future of the industry notes that about 90 percent of consumer transactions are still made in cash or by check.

So Visa and the other major card companies are targeting markets such as health care, supermarkets and fast food where credit cards have previously had little penetration.

American Express spokeswoman Gail Wasserman said her company's card holders have been able to "charge it" at some 1,000 Cineplex Odeon movie theaters since 1989.

A pilot program begun in November in Boston, in conjunction with the John Hancock insurance company, allows employees of participating companies to use American Express cards to handle their health insurance. Wasserman said the system not only pays the doctor but also files the insurance claim and bills the patient only for the amount not covered by insurance.

"Supermarkets have been a new focus for all the major credit cards and we're building a strategy," said Jody Hancock, MasterCard vice president of new merchant markets.

The grocery market is opening to credit cards, she said, because of "technology and (reductions in) the associated expense in relation to the margins at the supermarkets."

Several fast-food chains have also entered into pilot programs with major credit card companies, and Hancock said many will expand in 1991. MasterCard, for example, has widened its agreement with Arby's fast food restaurants to 22 cities.

Other new markets for credit cards, according to Hancock, are "transit type applications," such as commuter trains or subways, that would allow riders to substitute the need to buy tokens or provide exact change through a single swipe of a credit card through a machine.

Some local governments, she said, are also experimenting with systems that allow citizens to pay traffic fines or parking tickets and other fees with their plastic.

But are all these new uses going to add to the legions of Americans who are already over their heads in credit card debt?

Hancock said many of the new uses are too "small-ticket" to overburden most consumers and are aimed primarily at convenience.

"If the card holder gets into debt, it's not going to be the fast food burger that did it," she said. "It's going to be that piece of jewelry or that fur that they just had to have."