The cruise vessel Oceanos, operated by Epirotiki Line, has been booked almost to capacity on its seven-day luxury cruises of the eastern Mediterranean this season. But the difference between the summer of 1986 and the past dozen years is that instead of posting a passenger manifest that is 60 percent American, it showed less than 5 percent Americans when it sailed from homeport Piraeus July 11, and this trend kept up through August.

"We're getting to cruise on our own ships again," a Greek lady remarked at the captain's table the first night out. The captain smiled despite his realization that this was not improving the foreign currency reserves Greece so badly needs.On the Greek luxury cruise line everything is oriented toward American customers. All prices are calculated in U.S. dollars. Even the slot machines, set to pay off generously for the enjoyment of the passengers, accept only U.S. quarters. Although there are passengers from six or seven different language groups, English is the only language required of the crewmembers who come in contact with the passengers. Some stewards and hostesses do not even speak Greek.

Of the 23 Americans out of the 429 passengers on the mid-July sailing, nine were Greek-Americans. At the Greek island ports of call such as Rhodes, Crete and Mykonos, it was apparent that the tourists staying on the islands were virtually entirely European. This lone American journalist found no one with whom to compare notes. In Rhodes, I found a Greek-American liquor store owner, born in Pittsburgh but returned to the old country. He confirmed how bad business was without the relatively free-spending Americans wandering about. But his living expenses are so low that just selling a few bottles of premium scotch each day keeps him going.

There were some Canadians on the cruise, thought by the Greeks to be Americans until their frugal spending habits gave them away. The largest nationality of tourists was British. But without the Americans on the scene, the English-speaking sightseeing buses meeting the ship at its various ports numbered only two out of eight instead of the customary six out of eight. It was the Greek-language tour guides who did the biggest business with all the Greeks finally touring their own country.

There was a time when Europeans bemoaned the fact that Americans were threatening to take over their countries in the summer. Now tourist industry entrepreneurs are bitter about the lack of American visitors. Greece, in particular, usually is flooded with Americans out-buying and out-tipping all other nationalities for the best in food, wine, clothing, trinkets and accommodations. The English, French, German, Dutch and Spanish all together come in a poor second to the Americans who swarm over the Greek tourist attractions making hotel rooms almost impossible to book at the last minute.

Not so in the summer of 1986. The Amalia Hotels in Delphi, Olympia, Nafplion and Athens ran under 25 percent occupancy. These high quality hotels in top tourist areas depend on Americans to fill them up. This summer the staff of the hotels had to be cut commensurately, causing wide summer unemployment in the hotel industry.

"It's not fair," the Greek hoteliers, drivers, shopkeepers and restauranteurs reiterate bitterly. "There was no reason for President Reagan to tell Americans not to come to Greece. We love the Americans." And indeed they are learning just how much they do love the Americans during the summer the Americans stayed away. Suddenly they are acutely aware of the lost dollar pipeline and are sincerely redoubling their efforts to make the pitifully few Americans in Greece this summer feel comfortable and wanted.

At a heavily guarded July 4 reception at the U.S. embassy in Athens for top level Greek businessmen and government officials, the managing director of the Grande Bretagne Hotel summed up his summer booking situation succinctly. ''We never realized the sheer power of the president of the United States to turn off American spending in Europe. We certainly never before understood how obedient Americans are to the word of their president. In one sentence he wiped out our season."

While the third-rate hotels are filled with European tourists, it is the first class hotels patronized by affluent American visitors that are suffering this summer. The Hilton, the Intercontinental, the Marriott and other new luxury establishments are in serious trouble. There just aren't enough Arabs, feeling the oil pinch as they are, to take up the slack.

Adding to the problem is the steady weakening of the dollar. Nevertheless, the meals at the best restaurants are reasonable, a delicious and generous swordfish steak going for $10 and a bottle of good Greek dry white wine for $5.

It can hardly be denied that from the point of view of the Americans who did go to Greece this summer it had to be one of their pleasantest vacation or business travel experiences. Even the taxi drivers refrained from their once- notorious attempts to exact extortionate fares from their clients as they joined the national effort to impress visitors, particularly Americans, that Greece wants them back. "Tell the people back in America we love them," is the refrain.

As for the terrorist threat, the security of Athens Airport is stringent without being oppressive and this journalist wore a small U.S. flag with his name above it on the left breast of his trademark bush jacket with no trepidation whatsoever.

For the full story: Log In, Register for Free or Subscribe