For the past decade, Burl Willes has had the enviable project of tracking down the still-"undiscovered" islands of the Caribbean -- the kind of remote vacation getaways known only to the most savvy or adventurous travelers.

In his quest, Willes, a Berkeley, Calif., travel agent, explored more than 250 inhabited islands. Only about 60 met his primary criteria -- that they have no big hotels and no hordes of tourists. He favored, instead, islands that may have only one small guest house and no more than seven or eight small inns. Some of them you can get to by small plane; others only by ferry.

He picked 30 of these islands -- all of which he revisited this year -- to be included in a new guide, "The Undiscovered Islands of the Caribbean." It is scheduled to be published in early 1988 by John Muir Publications. The book is among several new guides or series of guides that make planning a Caribbean holiday easier now than it has been in the past.

If Willes has a favorite among the undiscovered islands he lists, it probably is Carriacou, one of the tiny Grenadines -- a chain of lush, beach-ringed islands stretching like steppingstones across the sea from St. Vincent south to Grenada. His description suggests the kind of idyllic places he was looking for.

"Carriacou is lovely, and it has everything," he says, with the enthusiasm of a critic who has spotted a winner and wants the world to know it. "It has varied flora and fauna -- a lot of tropical fruit trees -- and a charming town, Hillsborough. I always like a town to visit.

"I also like it because the people are still hand-making wood boats the way they did in the 19th century. And it has access to many deserted islands where you can go for the day if you want to be totally isolated."

Accommodations on Carriacou range from "a spectacular 200-year-old house for eight to 10 people," which rents for about $450 a week, he says, to a comfortable lodge room at about $25 a night.

Carriacou is one of five Grenadine islands that made it into his book out of a total of 11 that are inhabited. The Grenadines "have wonderful beaches -- and they haven't been over-developed. You might have a half-mile of beach totally to yourself." He finds the mountainous terrain far more appealing than the flatlands of other island groups.

The other selected Grenadines are Canouan -- "Its beaches are exquisite, probably the most beautiful in the Caribbean"; Union; Petit Martinique; and Mayreau, which, he says, has superb beaches and about 100 "hardy" residents.

Among the Grenadines that he excluded from his official list -- although they are mentioned as runners-up in the book -- are Palm Island and Petit St. Vincent, both privately owned luxury resorts populated only by the owners and their staff. "I wanted islands that had a small village," he says, so visitors can see how islanders live.

Another omitted island is Bequia, which has, he says, perhaps eight "tasteful" small hotels but "has been discovered by the international sailing crowd."

Among his other choices:

The Turks and Caicos Islands. A string of islands southeast of the Bahamas, they are "basically flat and not especially beautiful," he says, "but they have some of the most exquisite beaches and good scuba diving."

Marie-Galante. One of the French West Indies, located just south of Guadeloupe and linked to it by air, the sugar-cane-growing island "is not for everyone," says Willes. It's unlikely that you will find anyone who speaks English, and it is so unaccustomed to American-style tourism that "if you go to a restaurant, you have to give them an hour's notice so they can go out and buy food and turn on the generator." He has visited several times, staying in a small beach-front hotel and has "never seen another guest."

Coche and Cubagua. These two tiny Venezuelan islands south of the much larger resort island of Margarita are "for people who want to get away from everyone and everything," says Willes. Coche has one small hotel, and on Cubagua "you stay with the locals." What recommends them are their "super" beaches.

Montserrat. It is the largest of the islands included in the book and probably the one that has the most experience with tourists, though its hotels remain discreetly small. It was chosen, however, because of its waterfalls and mountainous geography.

Other recent books or series dealing with the Caribbean:

"Caribbean Ports of Call, a Guide for Today's Cruise Passenger," by Kay Showker (Globe Pequot, $14.95). The title is self-descriptive. The guide describes 24 popular ports of call for cruises of one to seven days that depart Florida for the Bahamas, the coast of Mexico and the northern Caribbean. Shopping suggestions, restaurants and walking tours of the port cities are included.

Insight Guides. A beautifully produced series of cultural and historic guides to nations of the world, the Insight Guide series has turned its attention to the Caribbean with large new volumes on the Bahamas, Barbados, Jamaica, Puerto Rico and Trinidad ($16.95 each).

Macmillan Caribbean. Another excellent series with titles dealing with Antigua, St. Lucia, Montserrat, the U.S. Virgin Islands, Cuba, Nevis, Curacao, Barbados, Jamaica and Trinidad and Tobago. The books provide good historical background and suggestions for sightseeing. From about $6.95 to $10.95 each.

Moon Publications. Two new publications in the international series aimed at independent travelers provide detailed background information about several Caribbean islands. They are "Guide to Jamaica," by Harry S. Pariser, which includes Haiti, and "Guide to Puerto Rico and the Virgin Islands," by the same author, which includes the Dominican Republic. They sell for $7.95 each.

"The Caribbean," by Frank Bellamy (Globe Pequot, $12.95). One of the Cadogan Guide series to international destinations, "The Caribbean" gives a quick once-over to the principal islands of the Caribbean, including lodging suggestions.

Caribbean Travel and Life. It's not a guidebook but a relatively new magazine focusing on the Caribbean. The September-October issue ($3.95) offers a well-written and very informative look at the Bahamas and spotlights "The Elegant Resorts of Barbados." Five issues a year sold by subscription or at newsstands.