Before you pay for emergency medical insurance for a trip abroad, check what services are covered by your major credit cards. Some provide emergency assistance for cardholders at no cost, often duplicating what insurance covers.

For some time now, the three major international credit cards -- American Express, MasterCard and Visa -- have provided travelers with such standard help as emergency check cashing and quick replacement of your card if your wallet or purse is lost or stolen. For many travelers, especially younger ones, this usually is enough protection if something goes wrong.

More recently, however, American Express and MasterCard have introduced programs that offer 24-hour hot lines providing referrals to doctors and lawyers abroad if you are faced with a medical or legal emergency. Another benefit is an up-front guarantee of hospital costs should you have to be admitted immediately. Some cardholders are even entitled to medical evacuation home if necessary.

Such programs have strong appeal to older travelers and to business travelers who go abroad frequently. It is important to know, however, that not every cardholder can expect every benefit in the event of difficulty.

In the case of American Express, for example, the extent of hot-line benefits is determined by whether you hold a green, gold or the expensive platinum card. The annual fee is $45 for a green card, $65 for a gold card and $250 for a platinum card.

With MasterCard, there also are differing benefits for regular and for gold cardholders. Only gold cardholders are eligible for the new hot line. In addition, not all banks or other financial institutions issuing MasterCard provide the full range of emergency benefits; so if you are a frequent traveler shopping for a new MasterCard, consider one that has traveler benefits. Annual fees vary, but a regular card averages $18 to $20 and a gold card about $35.

Here's a look at the new emergency medical and legal benefits: American Express: Last July, American Express introduced "Global Assist" for its green and gold cardholders. If you are traveling more than 100 miles from home, you can call a toll-free number for a referral to a doctor, hospital or lawyer throughout the world. If you left your prescription medicine at home, American Express will arrange for a new supply to be sent to you. It will advance you $5,000 for hospital admission (charged to your card). In a legal or medical emergency, it will forward a message to relatives or friends.

Platinum cardholders are enrolled in a program called Travel Emergency Services (TEA). It provides the toll-free referral service as well as substantially more benefits. If you (or a family member) are hospitalized abroad, a TEA-selected doctor in the United States will monitor your treatment, consulting long distance with the foreign hospital. If the TEA doctor does not think you are getting adequate treatment, TEA can arrange for you to be transferred to another hospital or back to the United States. If your children are with you, TEA will fly them home at no additional cost so they won't be on their own while you are incapacitated. If you are in the hospital for 10 days, TEA will fly a family member to your bedside at no charge. MasterCard: MasterAssist is the name given to MasterCard's new benefits package for gold cardholders (whose banks are participants). Like the American Express platinum program, it provides a 24-hour referral hot line for medical and legal emergencies. If you are hospitalized, a MasterAssist doctor will monitor your treatment via long distance. If you must be moved or returned to the United States, MasterAssist will provide transportation up to a maximum of $10,000. It provides $2,500 per person for medical costs or hospital admission. If you are hospitalized for more than eight days, MasterAssist will fly a relative or friend to your bedside at no charge. Most MasterAssist programs apply to cardholders and dependents.

Within the next few months, about 50 percent of the gold cards issued will have MasterAssist benefits, says Alan Schultheis, senior vice president for marketing. Unfortunately, MasterCard has no central number to determine which banks are offering them. Schultheis suggests phoning individual banks, keeping an eye on newspaper ads and checking the new card solicitations that come in the mail.

NOTE: Like any insurance policy, the new emergency benefit programs have very specific conditions that you must meet to be eligible. Before relying on the cards, make sure you know what is provided and who in the family is covered.

STANDBY FARE: British Airways has extended its off-season standby fare between Washington/Dulles and London through Aug. 31. Originally, the standby program was to be discontinued during the summer months.

The cost of a one-way standby ticket is $259, or $518 for a round trip. This compares to the airline's lowest APEX (advance purchase) fare -- beginning June 1 -- of $718 for a round trip on weekdays and $768 on Friday, Saturday and Sunday.

The standby fare is good any day of the week. Aimed at travelers who have a flexible itinerary, the ticket can be purchased any time; then you just show up at the airport on the day you want to leave. If seats are available, you fly to London; if not, you try again the next day. The procedure is the same on the return from London.

A day or two before you hope to depart, you can call the airline to determine if the flight still has space. The best chance for seating, according to an airline spokeswoman, is midweek.

BRITISH PAGEANTRY: Since this is an election year in Great Britain, visitors to London on June 25 will be treated to one of the country's most colorful pageants, the State Opening of Parliament. In nonelection years, the ceremony takes place in November, when most tourists have gone home.

For visitors, the big show is the queen's carriage ride from Buckingham Palace to Westminster to address Parliament and her return afterward. Each way, she is escorted by the Household Cavalry in great pomp. Traditionally, crowds jam the mile-and-a-half route along the Mall.

TEEN ADVENTURE: The National Wildlife Federation, an environmental organization, is offering a series of wilderness adventures this summer for teens, ages 14 through 17. The 10-day trips to the Blue Ridge Mountains of North Carolina feature a vigorous schedule of hiking and backpacking and a day of river rafting.

During their holiday, the young men and women who sign up are apt to acquire new self-reliance, plus a variety of outdoor skills and perhaps a greater appreciation for the natural world. The scenery is described as spectacular.

Participants will spend six days on a back-country hiking trip into the Shining Rock Wilderness Area of the Pisgah National Forest, covering about seven miles a day. The teens will be expected to carry personal items as well as a share of the group's food and its cooking and camping gear.

There will be opportunities for swimming in mountain streams, and those who are interested can take lessons in rock climbing. The final day is a raft trip down the French Broad River. Each hiking group is limited to 10 teens.

Departures are June 15 and June 30 from Asheville, N.C. The cost is $440 per person for food, instruction and gear. Travel to Asheville is extra.

For information: National Wildlife Federation, 8925 Leesburg Pike, Vienna, Va. 22184, (703) 790-4536.

FAMILIES WELCOME: A team of three women, each of them an experienced traveler and the mother of young children, has put together a selection of family tours called "Families Welcome!"

Among the tours are vacations in London and the British countryside and Paris and the French countryside. On these trips, hotels have been chosen that welcome children and have facilities for them. A big bonus for parents who want privacy is a separate room at certain hotels for the youngsters, offered at no extra charge when available.

For example, a seven-night stay at the Regent Crest Hotel in London (including round-trip air fare from New York and full breakfasts) ranges from $1,040 to $1,105 per person for adults (double occupancy). A second room for up to three children under 15 is free. Their air fare is additional.

The Regent Crest, which caters to families, is around the corner from Regent Park -- an excellent playground for active youngsters, say the tour operators -- and within walking distance of Madame Tussaud's Wax Museum.

On its foreign trips, Families Welcome! also provides a kit that contains detailed information on where to go and what to do in the cities and countryside as well as a guide to entertainment for the youngsters and their parents.

Other packages on this side of the Atlantic take families to a guest ranch in the Rocky Mountains; mountain resorts in Colorado and Vermont; and beach resorts in the Caribbean. A week's stay at the Paradise Guest Ranch in Buffalo, Wyo., ranges from $575 to $675 per adult and $475 to $525 per child, ages 6 to 12. Children under 6 are $190. Accommodations are in two- or three-bedroom cabins, and the price includes three meals daily and twice daily trail rides. If you like your horse, it's yours for the week.

Families Welcome! is operated by Dorothy Jordon, the editor of "TWYCH, Travel With Your Children"; Janet Tice, author of "What To Do with the Kids This Year"; and Susan Torn, publisher of "Kids Extra!/Paris."

For information: Families Welcome!, 1416 Second Ave., New York, N.Y. 10021, (800) 472-8999.

ON THE ROAD: Drive America's back roads and you might think the only radio shows being broadcast are gospel programs and on-the-air yard sales. To the contrary, says Natalie McClendon, the former manager of a public radio station in Nebraska -- and she's put together a list of U.S. radio stations to prove it.

McClendon says the airwaves are full of unusual fare that can, at times, provide a glimpse of life in the countryside through which you are passing. For example, one radio station in Lafayette, La., heart of Cajun Country, broadcasts in English and French, she says, with a mixture of Cajun, jazz, classical and "swamp pop" offerings. A station in New Town, N.D., is located on an Indian reservation and features contemporary and traditional Indian music. A station in the mountains of eastern Kentucky is operated by a regional arts center and programs good country music.

The three are among 1,100 public radio stations in the United States, including 40 that have been broadcasting since the pioneer days of radio in the early 1900s. To help the traveler discover this entertainment resource, McClendon has compiled a geographical list of public radio stations and their programming. Accompanying maps indicate the broadcasting area for major stations. This lets you know when you are approaching the closest place to tune them in.

Her book, "Go Public! The Traveler's Guide to Non-Commercial Radio" can also help you track down those illusive classical music stations that seem to fade minutes after you discover them on the dial. The book, at $12.95, is available only by mail order.

To order: Wakerobin Communications, 611 North 26th St., Lincoln, Neb. 68503-3030.