"If it's going to happen to you, it will -- no matter which airport you travel through," said Greek-born Vasiliki Tsaparlis on a Sabena flight to Athens.

But as Flight 845 from Brussels touched down Saturday at the Athens airport, Tsaparlis, 38, leaned over her 8-year-old son, Anthony, and whispered, "This is where the hijacking we saw all week on TV started."

Anthony, groggy after nearly 11 hours of travel, woke up, wide-eyed. "Where, Mom? On this plane?" he asked worriedly.

"No, no, son," she laughed, reassuring him.

The June 14 hijacking of TWA Flight 847 and President Reagan's warning against air travel to Athens have had an emotional impact on some visitors headed to Greece. They have also provoked an angry response from the Greek government and many of its citizens.

Hotels and travel agents report that many Americans have canceled vacation plans in Greece, and several passengers departing for Athens last Friday from Kennedy Airport in New York said they were concerned by the week's events.

"My grandmother is convinced she'll never see me again," said Ellen Feingold, 27, a retail buyer from New York, who was flying to Athens via Brussels.

Lara Janus, 17, a Liberty, Mo., exchange student on her way to Volos, Greece, said, "I'm not really worried, my mother is. They wouldn't send us if it wasn't safe."

Reagan's warning that Athens airport has "more than an average potential for terrorism" caused Pan American World Airways to suspend its daily flight from Frankfurt temporarily. The flight is to resume Friday, Pan Am officials said yesterday.

Greek newspapers reported last weekend that cancellations include 30 percent of cruise reservations, 1,200 reservations at the Intercontinental Hotel in Athens, 900 at the Hilton and 500 at the Grande Bretagne in Constitution Square. Pan Holidays, an Athens tourist agency that deals almost exclusively with Americans, reported a 60 to 70 percent cancellation rate.

A National Basketball Association all-star team called off two exhibition games in Athens this week, and the New York Philharmonic, scheduled for two sold-out performances Monday and Tuesday, backed out at the last minute, citing the State Department's advisory.

Greece's socialist government and Greeks of all political stripes have called Reagan's actions unfair and say they fear the impact on the country's tourist trade, which employs 300,000 people. About 575,000 Americans were expected in Greece this summer.

"Reagan's actions will definitely hurt our economy and the tourist trade in particular," said Christos Pasalaris, executive editor of Mesimvrini, a conservative newspaper.

Vasilis Milias, a businessman who supports the government of Andreas Papandreou, said, "I feel badly as a Greek. This hurts my country. It's touched a raw nerve."

And a lawyer, Cleas Panayiopakopoulos, who says he had a pro-Western orientation, added, "Reagan has gone a little too far."

Meanwhile, the Greek government has complained formally. Last Tuesday, the day after Reagan's televised news conference, Greek Foreign Minister Ioannis Haralambopoulos told Monteagle Stearns, the American ambassador to Athens, that Reagan's warning was "unjustified and unfriendly."

Transport Minister Evangelos Kouloumbis said the United States was "unfair" to single out Greece and added that airport security measures in Athens were equivalent to those at other European airports. According to Kouloumbis, two of 211 hijackings worldwide from 1978 to 1984 took place on flights leaving Athens. Forty-three hijacked flights originated in other European countries, 62 in the United States and 104 elsewhere, according to his tabulation.

To reassure travelers, a banner with bold green lettering hangs over the passport-control area at the Athens airport: "Greek Airports are Safe and Secure."

Tourists traveling despite the president's warnings paused to take photographs, and one Greek, glancing at a group of Americans, told his friend: "It looks as if they've written him off completely."

Many Greeks see a political message in Reagan's warning.

"It is quite clear by now that President Reagan's campaign against this country is politically motivated," said Leon Karapanayiotis, executive editor of Ta Nea, a pro-government newspaper. "Airliners have been hijacked from other airports -- New York in December 1984 and Frankfurt in February of this year come immediately to mind -- without the White House advising the American public against them."

Calling Reagan's advisory "provocative," Leonidas Kyrkos, the leader of the Greek Communist Party of the Interior, a party independent of Moscow, put it this way: "President Reagan is the best anti-American propagandist in this country."

In a pointed reference to last Friday's shooting at the State Department in Washington, in which a staff member's son killed her and then himself, Kyrkos added, "If I were in the position of Greek prime minister I would forbid the staff of the Greek Embassy to visit the State Department unless President Reagan applied appropriate security measures."

The dispute comes at a delicate time in the relationship between the United States and Greece. Prime Minister Papandreou, who has frustrated Washington since 1981 with his frequent criticism of the United States, was recently elected to a second term with a substantial majority. During his campaign, he said U.S.-Greek relations would enter "calmer waters" if he were elected.

"The whole thing comes at a bad time. The Greek government was very cautious during the elections not to show anti-Americanism," said journalist Nikiforos Antonopoulos. "But Reagan has tossed all this into the wind. How will this help improve the climate between the two countries? Won't it only exacerbate anti-Americanism? In the end, who loses? The tourist who heeds the president and flies to Belgium instead, only to get hijacked."