IN SAN JOSE, toward the end of the dry season, the weather was balmy -- a near perfect 75 degrees during the afternoon, dipping to about 60 at night. With the colon, the chief currency unit, floating, prices were half what they were just three months before -- 3 cents for a bus ride anywhere in the city, $3 or $4 for a several-course meal, less than $30 for a single room at a first-class hotel. Some of the most beautiful tropical beaches anywhere are just a $7 plane ride away.

Strange, then, that in April there was hardly another American tourist in sight in the capital city of Central America's wealthiest and most literate democracy. Troubling, too, for a country that counts tourism, at $90 million a year, as its third largest industry, behind only coffee and bananas.

Tourist officals in Costa Rica frankly admit that tourism -- particularly American tourism -- has declined significantly over the last two years, largely because of the fighting in nearby Nicaragua and El Salvador. Roberto Morales, assistant to the director of the Costa Rican Tourist Board, blames American newspapers which treat Costa Rica "as a state of a country called Central America . . . so we're at war supposedly." It's an ironic situation, he notes, considering that "some Central American countries call Costa Rica another state of the United States," so closely are the two countries bound by ties of trade and friendship.

For all that, Morales says Costa Rica's U.S. image was so bad for a while that the tourist board, in disgust, virtually discontinued its advertising in this country. But that quiescent phase is over, he says. Beginning this month, Costa Rica has launched a full-scale promotional campaign to lure back tourists -- a campaign featuring everything from newspaper advertising to junkets for travel writers and agents to tout Costa Rica's virtues as a recreational paradise.

I visited Costa Rica for 10 days within a week of the terrorist attack in San Jose on a group of American marines. The incident precipitated a rash of phone calls from anxious friends on the eve of my departure, asking me if I was still set on making the trip. I was already committed to going. Spanish dictionary and airplane ticket ($459 round trip from Philadelphia) in hand. My own anxiety was tempered by the thought that I would be visiting an American friend who, by virture of her year-long residence there as a teacher at an international school, would know enough to steer me away from possible danger areas.

Other potential tourists to Costa Rica, lacking similar resources, were noticeably less sanguine. Within a few days of my arrival, an international tennis tournamet was canceled. And a native tour guide told a fellow tourist and me enroute to a volcano that his agency had just been hit by a rash of cancellations by both American and Canadian tour groups fearing violence. That was the same week, by coincidence, that President Reagan was shot in Washington.)

My solitary companion on the volcano tour was a manager of rental property from Denver who was spending most of her time in Costa Rica braving poisonous snakes and fording waist-high rivers in the dead of night in the country's abundant tropical rain forests. This morning, however, we were after tamer stuff. Cameras in tow, we allowed our talkative host -- "I don't like coffee much," he told us, after informing us that it was his country's chief export -- to drive us in his red Datsun through coffee and banana plantations and around winding mountain roads to the edge of one of the country's major tourist attractions -- the increasingly active volcano Poas, which was conveniently belching multicolored gases.

The trip was a good introduction to two of Costa Rica's main splendors: its beautiful countryside, virtually unrivaled for scenic variety, and its people. Almost all are of Spanish decent -- unique among Latin American countries -- and they combine Latin warmth with a comforting familiarity with the English language, which is required in school. If any anti-American hositlity was present, it surfaced only in our guide's reckless driving. Fortunately, with buses and trains so cheap and gasoline outrageously expensive, there were relatively few cars on the road to collide with.

The volcano tour included door-to-door transportation, commentary and a stop for lunch, for about $20. Lunch itself was not included, but the small restaurant where we ate, along with a liberal population of flies, supplied chicken, potatoes, salad and a strawberry milkshake for under $2.50. The restaurant was actually an inspired improvisation, chosen by default because our guide couldn't find the one we were destined for, which was supposedly Swiss and clean (and expensive).

But no matter, Ticos, as they call themselves, lack the North American intensity about such trivialities as times and locations. What might -- to the North American sensibility -- pass as inefficiency pervades even the highest levels of the tourist bureaucracy, which is hampered by the fact that both prices and transportation schedules change almost daily.

I discovered that fact, to my chagrin, when I attempted to book the celebrated jungle train ride to the Atlantic Ocean port of Limon, a city known in part for its bustling drug trade. I waited for a travel agent who never returned; I tried to book a tour that no longer existed; and I finally ended up plunking down a painful $59 for a revised tour which was to take me only as far as the little town of Siquirris.

I waited for the tour guide the next morning, as per instructions, in the lobby of the elegant Gran Hotel, whose white facade is one of the landmarks of San Jose. In rushed a woman from the travel agency with bad news: the tour had bee canceled, since only one other tourist had booked it that day. But there was nothing to prevent the two of us from undertaking the trip together, the travel agent said, as she shepherded me back to the office to collect my refund. Sure enough, waiting there was my friend, the river-fordig rental manager from Denver.

Given the difficulty of planning anything in Costa Rica -- and making the plans stick -- it takes a spirit of adventure to enjoy one's trip here. A willingness to indulge in spontaneity leads to monetary, as well as spiritual rewards. By traveling to Siquirris on our own, my friend and I each saved approximately $54. Three dollars or so went for food, including snacks on the train, coffee i Siquirris and arroz con pollo (rice with chicken) back in San Jose.

The slow, lurching train ride through the jungle and across spectacular mountain scenery cost slightly more than $1 for four hours, and it was punctuated constantly by the cries of the vendors who passed up and down the aisles bawking everything from chocolate bars and mangoes to chicken on tacos. Most marvelous was their ability to adapt to the climatic shifts. As we descended into the lowlands and the air grew suddenly muggy, our vendors miraculokusly reappeared with watermelon and ice cream.

The only problem with this excursion is that once you get to Siquirris -- which would, in American western lingo, be called a one-horse town -- there's not much to do but turn around and go home again, this time by bus. The bus ride cost less than $1, but after an hour it grew dark and the road became bumpy, the only break in the monotony the sound of early evening rain signaling the beginning of the rainy season, which lasts from November to May.

The rental manager and I may well have been among the few tourists in Costa Rica that week. But there is a more or less permanent American -- a well as European -- community here, many of them pensionados, retirees lured by the low cost of living and generous tax breaks. "Costa Rica is New York in small," explained our Poas tour guide. You can run into just about anyone here, from an old college classmate to a Ba'hai missionary to a multilingual Dutch family who told us they came to Costa Rica because "here people have time for one another."

In a country -- and society -- so small, celebrities are everywhere and accessible. I ended one afternoon, devoted to the parks and museums of San Jose, in the new museum of Costa Rican Art. I was admiring the naturalistic sculptures of Fernando Calvos, when a jovial Tico informed me in Spanish that his mustachioed companion was none other than Calvos himself. I scoffed, disdaining to be taken for a gullible tourist. My sense of superiority collapsed when I checked out the larger-than-lie portrait of Calvos near the museum entrance: it was the image of the unassuming man who'd accosted me, broad mustache, gold tooth and all.

Such spontaneous encounters were my trip's main delight. A weekend excursion to the resort town of Quepos, with my hostess Joanne, was full of them. The Playa Mauel Antonio was lovely -- the water blue and warm, the white sand rimmmed by palm trees. But our second day there the tides were too strong for swimming. Jose, the Tico lifeguard who'd waved us out of the water, felt bad that he'd wrecked our recreation. So he and another friend, sort of a Tico Woody Allen, alive with self-deprecating wit, drove us in a jeep over dirt roads to a nearby finca (farm). There we gambled in our very own private river, overhung by shade trees and a rickety footbridge. Huckleberry Finn goes to Costa Rica, I thought contentedly. Except for the bevy of farm workers' children splashing about in the water, singing baptismal hymns in Spanish. And, later, the terrible case of tropical sunburn that confined me to my hotel for the evening.

Actually, my favorite encounter never really took place at all. My very first night in the country, Joanne's Tico housemate, Franklini, decided to take us to meet his friend Palacios, a Panamanian Indian whose Spanish promised to be incomprehensible (Costa Rican dialect is trying enough for an outsider) and whose English was nonexistent. Again, we drove up dirt roads, lost and late, to a magnificant ranch-style house, which commanded a stunning view of San Jose by night. The lights of the city stretched out along the country's central plateau below us, and the mountain air was chilly and exciting. Inside the house, we could hear the television set blaring. Unfortunately, after a half-hour wait, Palacios had yet to arrive.

His non-appearance seemed less surprising when Franklin described his most recent redezvous with his friend. During at typically peripatetic night, he and his friends had abandoned Palacios, promising to return. But, distracted by the strains of the salsa or a woman's smile, they had never come back, leaving Palacios waiting all night on a street corner, where he was at last picked up by police.

No matter, again. I like Franklin's dictum: Necesita la paciencia en Costa Rica" ("In Costa Rica, one needs patience"). And his reminder, in patient English: "Efficiency is not the same thing as effectiveness." Who better, after all, to draw such a distinction than a professor of public administration at the Univeristy of Costa Rica. CAPTION: Picture, Some of the most beautiful tropical beaches anywhere are just a $7 plane ride away from San Jose, Costa Rica.