They can admit it now that they've kicked the "charge-it habit."

"We were credit-card crazy," says Stephen O'Meara, 30, a letter carrier and part-time grocery clerk from Severn, Md. "We'd buy everything with credit cards," adds his wife Nancy, 29. "It was very easy to forget that we'd have to pay at the end of the month."

With his two jobs, Stephen O'Meara earned enough to pay their townhouse mortgage and buy necessities for his family of four. But even when Nancy O'Meara took a part-time job, they still couldn't pay off their $3,200 in credit-card debts.

"It was hurting our marriage, because we were always worrying about money," she recalls. "That's when we decided to call the Consumer Credit Counseling Service."

The O'Meara's problem -- resolved by tearing up their credit cards, switching to cash and working out a 30-month repayment program -- was less severe than that faced by most of the 200,000 people who sought help last year from the National Foundation for Consumer Credit.

"Our average client family earns $15,000 with a debt load between $9,000 and $10,000 in credit bills -- excluding mortgages, utilities and loans," says counseling service director Mary Quinn.

"With food, gas and utility costs going up people are using their credit cards to subsidize their incomes -- and that's when they get into trouble. About half the people who come to see us just need advice, about 40 percent need a debt-repayment program and 10 percent need legal help."

"There's no social, income or educational limitation on overextending yourself financially," adds counselor Marilyn Morgan of the group's Greater Washington branch. The nonprofit organization has 198 credit conseling centers nationwide, many of which have month-long waiting lists of people seeking free credit counseling and debt-repayment programs.

The 14,000 area clients range from welfare recipients to supergrades, and from grade-school drop-outs to Ph.D.s.

"At first I felt naked without my credit cards," admits Stephen O'Meara, who has been "card-free" since September 1977. "But it's a terrific program. wWe've cut back on some things, but we really enjoy whatever we do buy because we know there won't be a bill coming later."

Unlike the O'Mearas, an estimated 82 million American adults do carry credit cards which they use for 16 million purchases a day. Today's cards can be used to pay for nearly everything -- from local taxes to doctor bills, parking fines and groceries.

Each cardholder has an average of 7.1 cards -- totalling nearly 600 million credit cards in the United States, says H. Spencer Nilson, who publishes a newsletter for credit-card executives.

"Spurred largely by increased use of credit cards," writes Arthur E. Rowse in his "Help: 1980" consumer almanac, "total consumer debt rose a record 17 percent in 1978 to $1.2 trillion. By the end of the year, the average person owed $5,512."

"We are a nation of credit-card junkies addicted to popping plastic," sums up Rep. Frank Annunzio (D-Ill.), chairman of the House Banking Consumer Affairs Subcommittee.

The problem with credit cards, contends subcommittee staff director Curtis A. Prins, is that "they are no longer a luxury.

"You can't function in today's society, with few exceptions, without one. You can't get a check cashed in most places without a credit card. You can't rent a car (major companies require anywhere from 30 minutes to two days for a credit check if you don't use a credit card), and try checking into a hotel or motel without one."

A majority of card holders don't understand how finance charges, minimum payments and other costs are calculated, Prins claims, since card companies "purposely try to make it difficult for consumers to understand.

"They might as well be speaking a foreign tongue," he says, pointing as an example to a paragraph in the Master Charge agreement used by Northeastern Bank in Scranton, Pa.

"I don't think there's an intent to confuse anyone or hide anything," contends the bank's assistant vice president Donald Vermilya.

"I could explain it (the Master Charge agreement) to a person if we sat and talked it out, but it's not the same thing to put it in writing for them to understand. Most legal terminology required is not always readily understandable to the consumer."

Federal regulations "don't require that kind of goobledygook language," counters Prins who with two lawyers and a researcher couldn't figure out what the agreement meant. (For the existing version, and a translation, see the box at far left.)

Many card holders also don't realize that certain credit-card features may vary from bank to bank. "If a consumer shops carefully, spends time and asks questions," says Prins, "they'll find some banks more advantageous than others."

There are four basic categories:

Retail cards (Sears, Bloomingdale's etc.).

Usually honored exclusively by the issuing merchant, most retail cards extend a line of credit to the customer. Some require full payment at the end of the billing period, while others allow a minimum monthly payment with a finance charge levied on any outstanding balance.

Bank cards (Visa, Master Charge, Central Charge).

Bank cards are accepted by a variety of participating stores and service providers. Using a "buy-now-pay-later" plan, bank cards extend a line of credit to the customer and require a minimum montly payment. If the balance is not paid in full, a finance charge is levied.

Some bank credit cards can be used for cash advances. Some banks also offer debit cards which work like checks with participating merchants. Instead of tapping a credit line, the debit card causes the amount of purchase to be deducted from a deposit account.

Oil company cards.

Most cards are honored exclusively by the issuing merchant. However if there are none of that company's service stations in a particular geographic area, the card might be honored by another oil company. Details of these "interchange" agreements usually are listed on the back of the card.

While full payment is usually expected, an extended payment plan (with finance charges) often can be arranged.

Travel and entertainment cards (American Express, Diners Club, Carte Blanche).

Most travel and entertainment cards use a "pay-as-you-go" plan, with no pre-set spending limit. The full bill is due on receipt (although extended payment options may be offered).

T & E cards charge an annual fee of about $25 and feature extra services such as free traveler's checks, emergency cash facilities, overnight replacement service and separate cards for business and personal expenses.

(Finance charges and membership fees are both usually tax deductible.)

Along with an increased use of credit cards is the growing number of lost and stolen cards, notes Nilson, who estimates 3.5 million people lost 15.4 million credit cards last year.

Although federal law limits a customer's liability to $50 per card for unauthorized use, an increasing number of cardholders (nearly 3 million) are paying protection services to notify all their card companies about lost or stolen cards.

Companies such as the Florida-based Safecard Service, Inc., and the California-based Credit Card Sentinel charge $12 a year for registering a person's cards in their computer and providing an around-the-clock toll-free line for members to report missing cards.

January can be a particularly tough month for credit-card users, notes credit counselor Joanne Kerstetter. "All the Christmas-shopping bills are coming in," she notes. "And utility bills are higher."

Credit counselors, card companies and users offer this advice:

Don't charge if you can pay cash. Limit credit-card purchases to things you need and can afford, or to occasional one-time sale items.

Avoid spending more than 15 percent of you annual income on credit accounts. "If you earn $20,000 a year, for example, you can probably afford up to $3,000 in credit purchases.)

List every cent you spend for one month, keeping track of each credit-card purchase.

"Use credit cards intelligently," advises Alan T. Fell, Maryland's commissoner of Consumer Credit. "If you pay a bank-card bill when it's due to avoid a finance charge, you are, in effect, getting free credit. That's one way to beat the system."

Stick to one credit card if you tend to overextend yourself, says the American Bankers Association. When you reach your credit limit, stop.

Look for stores offering discounts to cash customers as an incentive to kicking the charge-it-habit.

Protect your credit cards as you would cash, warns the FBI. Be certain that all charge slips are completely filled out before you sign, make sure the card is returned and report theft or loss immediately.

Get help if you can't pay your bills on time. The Consumer Credit Counseling and Education Service provides free advice and debt-repayment plans (some offices charge a nominal mailing fee for debt-repayment programs). Call the Greater Washington office at 638-6996 or their local branches: Montgomery County 946-1011, Prince George's County 459-2121, Northern Virginia 591-9020. CAPTION: Illustration, no caption, by Chas. Addams; Copyright (c) 1976 The New Yorker Magazine Inc.