Immigrants from Puerto Rico characters in Bernstein and Sondheim's "West Side Story" sing their opposing opinions of that island in the sun:

Puerto Rico, you lovely island,Island of tropical breezes.

Always the pineapples growing,

Always the coffee blossoms blowing.

And:

Puerto Rico, you ugly island,

Island of tropic diseases.

Always the hurricanes blowing,

Always the population growing;

And the money owing;

And the babies crying;

And the bullets flying.

Unfortunately, U.S.-born travelers pick up similar mixed messages about Puerto Rico, and they don't know what the island is really like, says Margaret Zellers. For 10 years, she has written "Fielding's Caribbean 1988," and although the guidebook lists at least 30 Caribbean islands, she has chosen to go out on a limb (her words) for Puerto Rico.

"I don't normally do this for one particular island. In this case, I thought the Puerto Rico story was worth telling. We seem to take it for granted on the mainland."

The island is an outstanding tourist destination, she says, "because it has everything not only beaches, high-rise hotels and casinos in and near San Juan, but also one of the best-preserved sections of 16th- and 17th-century Spanish architecture in old San Juan."

Besides keeping the original forts El Morro and San Cristobal in good condition, the ancient, restored homes have been turned into shops, restaurants and apartments. Casa Blanca sits on the site of a house built for Ponce de Leon. The original thatched building burned in 1521. Stone ensured the longevity of the present house, started in 1523.

Ten minutes from old San Juan, the contemporary Condado section of San Juan has undergone a restoration, too. "When I first knew it, it was a luxurious residential area," Zellers said. Then the elegant resort hotels were built, but by the late `70s, the section had become seedy. After a massive cleanup, Condado has regained its original glitter.

"The Condado seems to have come into its own as a lively, action-oriented resort area along the lines of Miami Beach, Atlantic City and other gambling and sun-centered resorts."

The former Palace Hotel, after a $45 million renovation, reopened recently month as the Sands Hotel & Casino, claiming it has the world's largest free-form swimming pool bigger than the 1,776-foot-long pool at Puerto Rico's Hyatt Regency Cerromar Beach.

Still ahead is the completion of $17 million worth of renovations to the Normandie Hotel it will reopen as the Radisson San Juan and in the works are plans for three new properties.

Aside from glamorous resort hotels and sun-baked beaches, Puerto Rico has a few special advantages for U.S. travelers.

Because of its ties with the United States, visitors don't have to change currency. Dollars are acceptable everywhere.

Because of its Spanish heritage, you'll hear the cadences of the Spanish language everywhere, but you'll also find English spoken everywhere in the larger cities. At least a nodding acquaintance with Spanish would help those who venture into the countryside, where Spanish festivals and customs cling more firmly than they do in the cosmopolitan centers.

Zellers says the evening paseo in the park or plaza is still a part of village life. And although young men and women may not follow the "old country" pattern men strolling in one direction, women in the other they still gather to look at each other and possibly to meet.

There's also a karst region in the mountains, where limestone formations rise from the green landscape like tall, white conical candles.

In the eastern quarter of the central ridge, walking and hiking paths lace El Yunque, a tropical rain forest.

At Mayaguez on the west coast, an agricultural station affiliated with the University of Puerto Rico propagates extensive selections of tropical plants. Visitors are welcome to look and buy.

Arecibo, a two-hour drive west of San Juan, is home to the world's largest radar-radio telescope, with a dish 1,000 feet in diameter, covering 20 acres. Tours of the observatory are given at 2 p.m. Tuesday through Friday. Sundays, the observatory is open 1 to 4:30 p.m.

A museum in San German, about three hours southwest of San Juan, houses the island's largest collection of santos carved saints and holy figures.

Travelers out on the island can stay at a network of 15 paradores country inns patterned after Spain's parador system. Some are simple. Others have more elaborate facilities. The 53-room Parador Villa Antonio on the west coast has one- and two-bedroom apartments, tennis courts, a swimming pool, game room and playground for children.

Parador rooms range from $30 to $65 a night for two. Nine of the 15 paradores operate restaurants serving Puerto Rican cuisine, a mixture of Spanish, African and Indian cooking.

Even if you choose to stay in San Juan, you can sample Puerto Rican food at six other restaurants close to the city. They're part of a recently established network of gastronomic inns, which serve island specialties at moderate prices.

For more information, write the Puerto Rico Tourism Co., 1290 Avenue of the Americas, New York, N. Y. 10104 or call toll-free (800) 223-6530.

Another option, of course, is to consult Zellers' 780-page book; it's $12.95.

You'll find a chart in the front of "Fielding's Caribbean 1988," on which Zellers has charted desirable tourist facilities of the Caribbean islands.

Of the 30 islands listed, only Puerto Rico won stars (meaning "exceptional") in every category, including: good beaches, tennis, golf, sailing charters, scuba and snorkeling, good freeport shopping, local handicrafts, nighttime action, gambling, big hotels, small inns, memorable restaurants, special summer packages, cosmopolitan, quiet "away from it all," and good medical facilities.