Responding to American fears about traveling abroad after recent incidents of terrorism, some airlines, cruise lines and tour operators are eliminating or reducing penalties for canceling trips.

The travel industry hopes this relaxation of rules will encourage hesitant travelers to make reservations by reassuring them that if new attacks occur -- or their fears simply grow -- changing plans and destinations suddenly will not cost them money.

About 1.8 million Americans changed reservations for trips overseas earlier this year following attacks by terrorists at the Rome and Vienna airports last December. Nearly 80 percent of them either canceled their travel plans entirely or decided to vacation in the United States, according to a survey by the nonprofit U.S. Travel Data Center in Washington.

That survey ended in early February, and since then more terrorist incidents have occurred: A bomb exploded April 2 on a TWA jet en route from Cairo to Athens, a West Berlin discotheque was bombed April 5 (which led to U.S. air strikes on Libya and further threats against Americans), and a plot to blow up an El Al jetliner ready for takeoff from London April 17 was discovered and averted.

Only a few weeks ago travel agents were attributing an increased interest in trips to Eastern Europe to their clients' belief that those countries may be safer destinations because they are less likely to be the scene of terrorism attacks. Ironically, after the explosion April 25 of a Soviet nuclear reactor near Kiev, fears of possible radiation-induced illness caused many Americans to cancel plans to tour Russia, Poland and other nearby countries. The uneasy Middle East is another area that has lost bookings.

Until the recent rash of violent incidents overseas, airlines, tour operators and cruise lines have been relatively strict in enforcing penalties for cancellations of trips and changes in itineraries, but now they are being forced by circumstances to ease up.

"The only hope for . . . summer travel to Europe this year is for the airlines to eliminate advance purchase requirements so that clients can go there on an impulse," said Phil Davidoff, president and general manager of Belair Travel in Bowie, Md. Regulations covering the sale of APEX (advance purchase excursion) tickets generally stipulate that they must be purchased at least 21 days before departure, but penalties vary according to the airline and destination: A passenger who cancels a flight may pay as little as $25, or in some cases a percentage of the fare. Scheduled airlines sometimes have been lenient about making full APEX refunds if a passenger can document a genuine personal emergency.

Charter flights have their own rules, and a passenger who misses a flight for any reason may lose the full cost of the ticket (although insurance protection is available).

Package brochures indicate a variety of possible penalties on the land portion of tours, aside from those on the air fare: A handling fee is normally levied in the event of cancellation by the client (written notice may be required) up to a specified number of days before scheduled departure; a percentage of the total land cost also may be charged for a cancellation closer to departure, and the entire price could be forfeited unless the funds are refunded to the tour operator by firms -- such as hotels and sightseeing companies -- supplying the overseas services.

*The penalty for cancellation on most cruise lines normally ranges from $50 up to the full fare -- depending on the number of days left before embarkation.

Some tour packagers and cruise lines sell their own forms of protection against cancellation for any reason. Other travel insurance options covering sudden illness and other causes of cancellation are available from a number of companies, although until recently the threat of terrorism has not been included in those policies as specific grounds for a refund.

But now at least one insurance firm, Access America, has added a provision to its comprehensive travel protection program that permits buyers to cancel or interrupt international trips if terrorist activity occurs in a city within 30 days of their scheduled arrival date. The insurance reimburses travelers for prepaid hotel and transportation costsaccording to the level of coverage selected. The company, which added the provision last month, says it uses a liberal definition of "terrorism," but if necessary "will defer to the State Department for ultimate determination of whether or not an act was perpetrated by terrorists." Access America, a subsidiary of Blue Cross and Blue Shield, sells the policy through travel agents.

Major airlines that recently indicated they have eliminated or reduced penalties include:

KLM Royal Dutch Airlines. All cancellation and rerouting penalties have been waived until further notice.

Iberia. Cancellation fees are waived for flights to Rome, Athens, Tel Aviv and Cairo.

Aer Lingus. The Irish carrier will waive cancellation penalties "if it can be established that the cancellation is due to a fear of terrorism."

El Al. Penalties for rebooking an APEX fare are not being collected, but the airline charges a $100 fee if an APEX fare is canceled less than 14 days before departure without the trip being rebooked.

SAS. Penalties for the cancellation of APEX tickets are retained. The regular $100 penalty for changing an APEX ticket has been waived when changing to an SAS flight to another destination.

Cruise lines that are permitting nervous passengers to change their minds about sailing without forfeiture of payments, or which are selling their own cancellation protection, include:

Sun Lines. This line applies the full value of any canceled cruise aboard its two vessels in the Mediterranean to a future cruise embarking within one year.

Holland America Line. A cancellation fee waiver has been sold for a few years. To avoid charges, prospective cruise passengers pay $49 per person and are required to notify the company in writing of their decision not to sail no later than 24 hours prior to departure of the ship -- or plane, in the case of a fly/cruise package.

Royal Viking. Last November the line instituted a fee waiver program charging $50 per person to eliminate all penalties usually assessed, provided that a passenger notifies the company of cancellation by phone or in writing no later than 24 hours before scheduled departure.

Tour wholesalers who operate nationally with a high volume of business, and those that have a well-established relationship with reputable overseas hotels, can be more relaxed about cancellations, according to travel agent Davidoff, because the deposits required of them are probably not high and do not have to be forwarded far in advance.

Smaller wholesalers might have to pay a high percentage of the package price as a deposit for accommodations booked months before scheduled departures. Or they may be required to forward deposits to the suppliers far in advance to guarantee that the blocked hotel space will be held for future guests, or to negotiate lower rates. And so they often must send off a major portion of advance payments received from clients. If these operators are not still holding the funds when a client cancels after the cutoff date, and no replacement client can be found to go on the tour, the entire land cost of the package may be forfeited.

Under ideal conditions, both the packager and the hotel will try to be flexible because they are looking forward to future business from the customer. "They shouldn't forget about tomorrow," said Davidoff.

Among tour operators making it easier for travelers to cancel:

American Express. Cancellation fees are waived on the land portion of all packages to Europe, the Middle East, Africa and Russia for "tour clients who have concerns" about traveling abroad at this time. The firm is encouraging customers to consider other destinations, but will refund all costs exclusive of APEX penalties.

Globus-Gateway/Cosmos. Customers who have purchased a European tour are being allowed to change without penalty to another area of Europe; or, if they wish to switch to another continent, they may choose a comparable package to the Orient, the South Pacific or even North America.

Trafalgar Tours. With packages scheduled for both Western and Eastern Europe, the firm last November began offering a $15 cancellation protection plan to permit travelers to drop out for any reason. A spokesman said the plan is not a consequence of terrorism but was devised as a consumer incentive and is being purchased by most of its clients. It covers only land arrangements.

Caravan Tours. The company has maintained a full refund policy for 30 years as a goodwill gesture. It allows its clients to cancel, up to the day of departure -- for any reason -- any of its packages to Europe, Africa, the Soviet Union or the Orient. The entire land cost is refunded through the travel agent, who must still charge any penalty due the airline.

Maupintour. A cancellation plan for $30 per person is being offered for the fourth year as a basic service to consumers by this packager of upscale tours around the world. "We've found that most people are considerate and inform us of cancellations as early as possible," said the wholesaler.

General Tours, one of the largest U.S. wholesalers of packages to the Soviet Union, which had decided not to offer its programs to Israel and Egypt this year, reported losing many bookings to Eastern Europe immediately following the nuclear accident. Another American tour wholesaler, the Russian Travel Bureau, was also hit by cancellations along with other New York operators, though it had substituted Tbilisi in place of Kiev on tours to Moscow and Leningrad. Both firms say the number of cancellations has now dropped.

Intourist, the Soviet government travel agency, agreed to forego cancellation fees -- as did some airlines that fly to Russia -- for a brief period, but regular penalties are again in effect.

The State Department, while not advising against travel to the Soviet Union orEastern Europe, issued a travel advisory notifying Americans to avoid visiting Kiev and adjacent areas. (It also had advised women of childbearing age and children not to go to Poland, but later withdrew that warning.) Public Health Service has suggested that visitors to Poland take certain precautions -- such as avoiding fresh milk and cheeses, drinking only bottled water, and washing fresh vegetables and fruit with bottled water.

It is always advisable when booking air travel or tours, whether directly with an airline or through a tour operator or travel agent, to ask what cancellation penalties -- and insurance possibilities -- are currently in effect and what is the time limit or cut-off date. All procedures, especially those instituted recently in response to concerns about terrorism, may be changed without notice.