The recent hijacking of an Egyptian jetliner en route from Athens to Cairo has thrown into sharper focus efforts by major corporations to protect their top executives from terrorists while traveling abroad.

Reacting to the threat, corporations around the country are consulting security experts -- both within and outside the companies -- before finalizing travel plans. They are warning employes about potential dangers, canceling some tours for executives and customers -- or switching to destinations that seem less hazardous -- and trying to make their overseas facilities and personnel less-attractive targets. Some firms are asking agents to book their officials under fictitious names and no longer want airline ticket jackets customized with their company logos.

The travel industry was jarred for the third time in five months by the tragedy at Malta's airport on Nov. 23, where an American woman was executed by the terrorists and 58 other passengers, crew members and hijackers were killed when Egyptian commandos stormed the plane.

Just one month earlier, the Italian cruise ship Achille Lauro had been hijacked in the Mediterranean. That incident, in which an American passenger was killed by terrorists, followed the hijacking in June of a TWA flight after it took off from Athens. A U.S. Navy diver on the jet was slain.

After the TWA incident, the U.S. government advised Americans not to use the Athens airport and anxious travelers canceled their travel plans, costing Greek tourism about $300 million. (The airport later was declared safe by the International Air Transport Authority.)

In addition, a number of Americans decided not to take previously booked Mediterranean cruises following the Achille Lauro incident because the cruises originated and ended in Athens, and other cruises were canceled because of concern expressed by clients and travel agents. In fact, Sea Goddess Cruises, whose two 116-passenger vessels cater to a very upscale market, recently announced it has canceled all its sailings to both Egypt and Israel next year and is cutting 1986 sailings from Athens and Rome by 40 percent.

Despite these events and lingering uneasiness, the vast majority of U.S. tourists have completed their vacations abroad this summer and fall with no difficulties more serious than occasional missed connections and lost baggage. There is no way to accurately measure how leisure travel has been affected so far, but the chance of the average tourist being involved in a terrorist action remains minimal.

However, the recent tragedies have caused some business travelers to take more precautions. Among the indications of increased concern about terrorism:

*A conference on "Terrorism, Tourism and Traveler Security" will be held Feb. 12 through 14 at the D.C. Convention Center.

Sponsored by Antone Security Inc. (P.O. Box 409, Bowie, Md. 20715), a division of an international security firm, the conference is directed at corporations, travel agents and foreign tourist offices in this country. It is also open to the general public. Admission to the three-day meeting is $450 per person.

"We hope to convey, in a nonalarmist manner, the need to consider security when making travel arrangements," says Jerry E. Hoffman, president of Antone. He is a former Air Force counterintelligence officer who also has worked for the CIA.

Among the speakers scheduled to address the meeting is Martin Shugrue Jr., vice chairman of Pan American World Airways, who recently singled out terrorism as "the most critical issue facing our industry." Other scheduled speakers are Hoffman; Robert Hogan, assistant vice president for international security, Bankers Trust Co. of New York; Eugene Mastrangelo, senior analyst, Risks International of Alexandria;; Joseph Hallissey, chairman and chief executive officer, the American Society of Travel Agents; and Vince Hodgins, director general of the Mexican Tourism Office in New York. Donna Tuttle, undersecretary of commerce for travel and tourism, will give the keynote address.

*Antone Security is one of a number of firms in the specialized field of travel security for private and corporate clients. It is the Houston-based subsidiary of the Etropolitan Group of companies of Bournemouth, England, and also has an office in Athens.

Other companies involved with corporate security include Control Risks Ltd. of Bethesda, the main overseas office of a London-based firm, which also offers clients direct access to its computer data base by country for the latest assessments of risk; and Wackenhut Corp. of Coral Gables, Fla., whose 42 overseas subsidiaries and affiliates help its Executive Protection Division provide information on terrorism and supply armed escorts in high-risk areas where permitted by local law.

Antone performs various services for business firms, including designing high-tech computer systems to ensure their security, as well as the retrieval and storage of sensitive documents. Travel services involve training corporation personnel who travel abroad and researching destinations selected for executives' business trips. If Antone handles the security for a specific trip, they survey hotel and other facilities in advance of arrival, establish coordination with local police and provide Antone security personnel to accompany the group.

Hoffman uses Risks International, a security consulting firm that analyzes terrorist activity around the world and publishes its findings for clients weekly, monthly and quarterly. The information is an aid in making assessments of the political and terrorist threat to prominent executives who may be valuable targets abroad because of the work their companies perform. Risks also is conducting security surveys of U.S. firms to determine the vulnerability of their facilities and recommend corrective action.

Eugene Mastrangelo, Risks' senior analyst, says its continually updated computer-based data system holds "over 22,000 incidents of terrorism since 1970" and helps the company to project "where the level of threat may increase." Travel security is only one facet, Mastrangelo says, but "there is a growing awareness among terrorists that intimidating tourism is one good way to punish a government."

*Pan American World Airways' traffic to southern Europe dropped sharply after the TWA jet and Achille Lauro were hijacked, according to John Krimsky Jr., senior vice president of marketing. Pan Am officials estimate that nearly half of their passengers changed their itineraries and flew instead to countries in eastern Europe and even South America.

*The American Society of Travel Agents last month held its World Travel Congress in Rome under the tightest security in the organization's 55-year history.

About 7,000 ASTA delegates, including top corporate officials from airlines, hotels, cruise lines and government tourist boards, met while armed military units and police kept the group under constant surveillance. Roads were cordoned off and only officially marked vehicles were admitted, delegates had to pass through metal detectors, and police dogs sniffed packages for bombs.

For the first time, the registry of delegates did not show what hotels they had booked. (ASTA's 1980 congress in Manila was canceled after a bomb exploded at the opening session.)

*Incentive tour groups have either canceled trips or changed their destinations recently to areas considered less hazardous.

An incentive tour is a trip sponsored by a company as a reward for employe or dealer performance. In one case, a group of 1,100 dealers who originally had planned to fly to Rome last Monday received a few hundred cancellations, and some passengers were rebooked on tours being run concurrently to Barbados. In another, an incentive tour group of corporation executives -- 150 people including spouses -- canceled a $450,000 package trip to Athens and the Greek islands scheduled for July after studying a report prepared by Antone Security.

Antone's Hoffman had been contacted in May by the Silicon Valley firm -- all cases are handled confidentially and Antone does not release clients' names -- to research the risks of their annual "Presidents Tour" and make recommendations. Security experts already had concluded there were serious concerns about the tour before the TWA hijacking occurred and strongly advised against the trip.

*Texaco Inc. is depending upon cooperation between its travel and security departments to minimize the threat to its employes. (One was killed in Teheran, Iran, and one was kidnapped in Bogota', Colombia, and died during a rescue attempt. Another was kidnapped in Ethiopia and later released.)

"We're targets for terrorism because we're an oil company doing business in areas suffering from political unrest," says Harry Versen, Texaco's travel manager. "When we have a directors' trip, a security firm will give us an appraisal of risk factors, which is then reassessed by our own security people. But if we were to give out a general red alert on everything that comes in here, no one would go anywhere. You can't live in constant fear," he adds.

Versen reads State Department advisories, checks airlines' computer reservations systems for notes to agents about adverse conditions and also studies Interpol reports that give profiles of terrorists and discuss risk factors in various areas. He alerts employes about national holidays in certain parts of the world where he believes public demonstrations could erupt into violence directed against foreigners.

*E.F. MacDonald, which describes itself as the largest incentive tour operator in the world, has urged all its ground operators "to put pressure on their governments and airport authorities to make sure security is good," says President Richard Fordyce.

Fordyce added that "our company would take a very strong stand against travel to any country that chose to disregard security precautions, had substandard controls or been indifferent to terrorists' threats, or any country that badmouthed the United States."

E.F. MacDonald is a division of the Carlson Companies, a conglomerate that owns the Radisson Hotel chain, Ask Mr. Foster travel agencies, Cartan Tours and First Tours; is the largest travel agency owner in Canada and also operates tours in Mexico and Hawaii.

*The House Merchant Marine Subcommittee has held hearings on measures to improve security on cruise ships and at ports here and abroad. Some cruise lines already have tightened security.

Congress has been considering whether a uniform system of security can be established in this country for cruise lines as has been done for the airlines. There is no federal law to protect ports or passengers. No further hearings are currently scheduled.

*Lawyers have advised travel agents to protect themselves against lawsuits by disclosing any information about developing problems or unstable conditions in an area, and then letting the clients -- whether corporations or individual travelers -- make up their minds whether to go.

Jerome Sherman, president of Travel Forum in Palo Alto, Calif., told a recent meeting of U.S. agents in Monaco that his agency's ticket jackets warn that passengers are traveling at their own risk. In a telephone interview, Sherman said that one major corporation recently rejected a Nile cruise he had suggested for an incentive trip and was also reluctant to consider Israel. Finally, a European destination was chosen.

Any traveler can phone the State Department's Citizens Emergency Center, 632-5225, for advice on possible dangers due to political unrest or terrorist threats abroad. One of the latest travel advisories concerns conditions in Khartoum:

"Due to the presence in Khartoum of known terrorists and possible threats to U.S. interests, American citizens are advised to avoid the Sudanese capital . . . "