The events have come in rapid succession in 10 days of terrorism: a hijacking in Athens, a bombing in Frankfurt's busy international airport, a possibly sabotaged jumbo jet falling in pieces into the North Atlantic, an exploding suitcase in Tokyo's Narita airport.

The victims were vacationers, business travelers, military personnel between assignments, airport workers and average individuals off to see their families. Although the terrorists presumably acted with political or religious purpose, their victims appear to be randomly selected. Their fates challenge the fundamental assumption that has made air travel indispensable to the modern age: that it is safe to fly.

Although the hijacking and bombings may prove to be no more than coincidentally related, they have caused great concern. Top federal airport-security officials and representatives from the U.S. airline industry met yesterday afternoon at the Federal Aviation Administration to compare notes on what they know and to ask, as one of them said afterward, "Are we doing enough?"

Rodney Wallis, security director of the International Air Transport Association (IATA), which represents 138 international airlines, called an emergency meeting of the group's security advisory committee for this week to discuss the Air-India disaster.

"There's nothing we can do here until we start to get some real facts," an IATA spokesman said.

U.S. experts are concerned that the terrorist type of hijacking or bombing presents a more challenging problem than the "homesick Cuban." For one thing, many security techniques today assume that no one is suicidal.

If a religious fanatic believes that his reward is in the beyond, that adds a different element to the equation. Secondly, after a hijacking occurs, a well-backed terrorist is more difficult to deal with than an individual or a small group. With an individual or small group acting alone, "You can wear them down and eventually get everybody off safely," a specialist said.

Every day, U.S. airlines carry about 1 million people on 15,000 flights, including about 500 international flights. Considering the numbers, the odds of being hijacked or blown up are infinitesimal.

Nonetheless, a series of events such as those in recent days makes the odds unimportant for many people. After President Reagan said the United States regards security at the Athens airport as inadequate, 30,000 Americans backed out of bookings to Greece, according to a survey by Knight-Ridder newspapers.

The United States has developed both simple and sophisticated responses to the threat of hijackings and bombings. Some of those techniques are obvious, such as the metal detectors passengers must walk through before boarding. Some are unseen, such as the "hijacker profile" that has been developed to help airline employes prevent trouble.

Several "classified" techniques for screening passengers, baggage and cargo have been developed and are used to reduce the likelihood that the terrorist or the kook will endanger the rest of us.

After the hijacking of Trans World Airlines Flight 847, FAA officials urged airports and airlines around the country to be especially alert to the "copycat syndrome," because experience has shown that hijackings beget hijackings.

For years, pilots have been a major force lobbying for improved security. The Air Line Pilots Association's threat of a nationwide strike after a rash of Cuba-related hijackings in the early 1970s led to the establishment of the FAA's aviation security office, which is regarded even by the pilots as top-notch.

But the threat is changing.

"We're looking at a very unstable world at the moment," Steve Last, principal vice president of the International Federation of Air Line Pilots Associations, told United Press International in London. Events are occurring so rapidly, he said, that it "gives cause for grave alarm that the air industry is under attack."

As in all endeavors, there is no such thing as total security. And reputations don't mean a thing. TWA has been known within the industry for years as having one of the best security programs. Canada and West Germany are regarded as countries where you can depend on the airports and the screening procedures to produce safe flights.

On the other hand, southern European countries, particularly Italy and Greece, have had a reputation for sloppy security. All countries have the equipment and the knowledge to thwart most hijackers or bombers, largely through the information exchanged through the IATA and the International Civil Aviation Organization.

Security ultimately "gets down to a question of human performance, of attitudes," one U.S. expert said last week.

Last year, there were five hijackings and seven unsuccessful attempts on U.S. airplanes and 21 hijackings of foreign carriers. Since 1950 there have been 80 explosions aboard passenger aircraft, 22 of them on U.S. airlines.

Although it has not been established that a bomb caused the Air-India crash, which apparently killed all 329 people on board yesterday, that is the most logical explanation for debris scattered over 4.5 square miles of ocean.

Only one other Boeing 747 has ever disintegrated in a similar fashion. That was an Iranian Air Force plane that crashed near Madrid in May 1976, killing all 17 aboard. Lightning is officially blamed as triggering that event, but that conclusion is highly controversial and many experts list the cause of that crash as unknown.