If you are vacationing in Europe and decide to phone home, you could be in for a shock. An unpleasant fact of travel is that many foreign hotels add a surcharge to the cost of long-distance telephone calls made from a guest's room.

"Unwary Americans traveling abroad for the first time are stunned to learn that surcharges of up to 300 percent and more have been added to the cost of an international call by the overseas hotel," warns AT&T, which has just announced a new plan aimed at curbing surcharge abuses.

The program, called Teleplan, is a high-powered effort by AT&T to get foreign hotels to limit the amount of surcharge on long-distance calls to no more than $1 a call.

Teleplan is linked to another AT&T international phone service called USADIRECT. Introduced in 1985, USADIRECT makes it possible for Americans traveling in 32 countries to pick up a phone and reach an English-speaking AT&T operator in the United States without having to go through a foreign operator.

Together, Teleplan and USADIRECT are designed to ease both the cost and the inconvenience of phoning home from a foreign country.

As an example of excessive surcharges abroad, Judy Arenstein, AT&T international marketing manager, cites the experience of an American doctor traveling in Paris who phoned his office in Los Angeles to check on a patient. "The hotel billed the physician $159 for the $57 call," she told a Teleplan press conference in New York.

Other examples: A businesswoman phoning from Hamburg in West Germany to Rochester, N.Y., was charged $82.50 for a 10-minute call that should only have been billed at $15. A couple making a $19 call home from Italy had to pay an additional $57 for the surcharge. An AT&T official -- even they can get caught unawares -- made a series of long-distance business calls from his New Delhi hotel room. His bill, according to AT&T, came to $1,000 -- half of which was the surcharge.

To counter this longstanding problem, AT&T has embarked on a campaign to enroll foreign hotels and hotel chains in Teleplan. Those that subscribe promise that any surcharge they add to a long-distance call will not exceed $1 per call, no matter how long the call lasts. In other words, you pay the standard long-distance fee for your call plus (at most) a $1 fee charged by the hotel.

To date, the only chain that has signed up is Holiday Inn Asia-Pacific, which has 30 hotels in 11 countries. But an earlier version of Teleplan, created in 1976, enlisted 13 hotel chains and a total of about 900 major hotels. AT&T is currently attempting to renegotiate Teleplan contracts with these hotels and others. The original Teleplan required participating hotels to cap surcharges at no more than $10 per call.

As a lure to the hotels, which must give up what can be substantial income from surcharges, AT&T has promised a major advertising and public relations campaign alerting the public to Teleplan hotels. Business travelers especially, it is believed, may be attracted to a hotel that promises not to mark up the price of phone calls.

The second component of Teleplan, AT&T's USADIRECT service, is designed to make placing a call from abroad easier. It operates in two ways:

In 10 countries and territories, callers can pick up practically any phone and, by dialing a special access code, be connected almost immediately with an AT&T operator in the United States. The operator will place the call, and it will be billed at standard, operator-assisted rates. The call can either be charged to an AT&T Card or made collect.

This service is available from Australia, Belgium, the British Virgin Islands, Denmark, France, West Germany, Japan, the Netherlands, Sweden and Great Britain.

Each country has a different access code. A plastic, wallet-sized USADIRECT card listing the codes can be obtained by contacting AT&T at (800) 874-4000, extension 201. Information about obtaining an AT&T Card also is available at this number.

In 22 countries and territories, USADIRECT service is available from special phones. Clearly identified, they are located in the lobby of hotels that have joined the Teleplan program as well as in airports, seaport cruise docks, telephone centers and U.S. military bases. By picking up one of these phones -- no need to dial an access code -- the caller will get an operator in the United States, "often within 30 seconds," says AT&T. The call can be charged at standard, operator-assisted rates to an AT&T Card or made collect.

This service is available from Antigua, the Bahamas, Bahrain, Barbados, Bermuda, the Cayman Islands, Colombia, the Dominican Republic, Ecuador, El Salvador, Guatemala, Hong Kong, Jamaica, Japan, Korea, Panama, the Philippines, Spain, St. Kitts, St. Lucia, Trinidad and Tobago, and the Turks and Caicos Islands.

By using USADIRECT, says AT&T, the traveler abroad "can avoid the frustration of an unfamiliar telephone system and linguistic barbed wire ..."

To protect yourself from excessive surcharges in the likelihood that, at least for now, you are not staying in a Teleplan hotel:

Make sure you know what, if anything, the hotel charges for handling long distance calls before you make one.

Consider using a pay phone, either in your hotel or at a public telephone center. The centers often are staffed with English-speaking operators.

Call home from your room, but be brief about it. Ask the party at home to call you back and hang up immediately. Since the surcharge is usually a percentage of the long-distance rate on an outgoing call, you will be billed only for the few seconds you were on the phone. There is no surcharge on incoming long distance calls.

For more information about Teleplan and participating hotels, contact the AT&T number listed above.

ANGKOR WAT: Forbidden to visitors for more more than a decade, the famous ruins of Angkor Wat in Cambodia have been included in an unusual Southeast Asian itinerary offered in 1988 by a U.S. tour operator.

Travcoa of Newport Beach, Calif., which has featured luxury trips to exotic destinations for 33 years, plans a series of 22 two-week excursions to Thailand, Ho Chi Minh City (formerly Saigon) in Vietnam and the ruins of the walled and moated city of Angkor Wat in Cambodia.

The stop at Angkor Wat will be on a day-trip only, made by charter jet flight from Ho Chi Minh City. Participants will have five hours to tour the so-called "lost city" of the 14th- and 15th-century Khmer kings as well as the temples of nearby Angkor Thom. The group will then return directly to Ho Chi Minh City.

Some U.S. tour operators began offering escorted tours to Vietnam this year. Travcoa's day-long excursion into Cambodia is one of the first opportunities American tourists have had to see Angkor Wat since the Vietnam war.

Travcoa president M. William Dultz visited Angkor Wat in May and went back again in September. He found the ruins in an excellent state of preservation. "Angkor still stands as imposing as I remember it some 30 years ago," he writes in Travcoa's 80-page, magazine-sized catalog of 1988 tours.

The Cambodian people "welcome American visitors back to their country," according to Travcoa.

Tours depart about twice a month from Feb. 3 through Dec. 28. Each is limited to 25 participants. So far, "they've generated a tremendous amount of interest," says spokeswoman Pat Petit-Clerc.

On the itinerary are six days in the Thai cities of Bangkok, Chiang Mai and Chiang Rai; three days in Ho Chi Minh City; a day at Angkor Wat; and another day in Bangkok. The land cost is $2,195 per person. Air fare from the West Coast is approximately $1,466, and the charter flight to Angkor Wat is another $400.

American citizens are not prohibited by the U.S. government from visiting Vietnam and Cambodia, but the State Department has issued "travel advisories" concerning both countries. It cautions that the United States does not maintain diplomatic or consular relations with them, and no third- party nation represents the interests of the United States in either.

"Consequently," say the advisories, "the United States government is not in a position to accord normal consular protective services to U.S. citizens," and it "discourages" travel to Vietnam and Cambodia. The U.S. Treasury Department sets strict limits on the amount of money Americans can spend in the two countries.

For information about the tour: Travcoa, 4000 MacArthur Blvd., Suite 650E, Newport Beach, Calif., 92660, (800) 992-2003. For information regarding State Department travel advisories: Citizens Emergency Center, 647-5225.

GETTING ORIENTED: Three hotels in Japan have put together a free information packet, "How To Get Oriented in Japan," designed for American tourists or business travelers headed for that country.

The packet includes large, full-color street maps of Tokyo and Kyoto, a "tourist map" of Japan and a 30-page booklet of tips for touring Japan. The booklet lists, for example, nine English-language guidebooks to Japan picked as the best resources for tourist information before you leave home.

It also offers very helpful advice, such as suggesting visitors take the "direct bus" to their hotel from the airport rather than a cab. In bold print, the booklet warns, "Cabs are expensive." Should you take a cab anyway, it notes that taxi doors open on the left side only, and the driver operates the door locks.

On the subject of Tokyo subways, it advises that "if you are confused about which subway ticket to purchase, select the cheapest one and pay the attendant the difference when you leave the subway station." Don't, it warns, take the subways and trains between 7:30 and 9:30 a.m. and 5 and 7 p.m. In rush hour, "the crush of humanity is awesome."

The packet is distributed by the Westin Akasaka Prince Hotel, the Tokyo Prince and the Westin Kyoto Takara-ga-ike Prince hotels. Another booklet describes all 48 urban and resort locations of the Prince Hotels chain. For a copy: Prince Hotels of Japan, 230 Park Ave., Suite 906, New York, N.Y. 10169, (800) 542-8686.