Question: How do you turn a quaint little Mexican fishing village into a modern resort without ruining it? Answer: You put all the modern tourist facilities down the beach a few miles, and you leave the little fishing village alone.

Does it work? You bet it does.

This is what Fonatur, the Mexican tourism development agency, has done with the new vacation place on the Mexican Riviera, the resort of Ixtapa-Zihuatanejo. It's hard to say, but it's easy to enjoy.

Sometimes called "Cancun West" Ixtapa-Zihuatanejo is a couple of years behind Mexico's showplace Caribbean resort of Cancun on the Yucatan Peninsula, and the development on the Pacific coast is on a smaller scale. But it is ready. And it is super.

The formula is simple, and you wonder why it has not been done before. If you want to enjoy modern resort facilities, such as new hotels, tennis and golf, they are available at one location. If you want to poke around the unspoiled antiquity of a real Mexican town, that's available about 6 miles away. The two are not mixed.

Zihuatanejo (see-whah-tah-NAY-ho) is the old fishing village on a bay about 150 miles north of Acapulco. A modern jetport is nearby - not too close but not too far - with plenty of flights by both Aeromexico and Mexicana Airlines. The town has grown some as the tourist development has taken place, mainly to provide housing for those who work at the resorts.

But Fonatur has ruled out new buildings and other development at Zihuatanejo. The town retains its rustic charm and still is basically the same little village it always has been. No new hotels. No tennis courts. No golf course. No neon, no glass and concrete towers. It is a compact enclave of shops, restaurants, small hotels, offices and homes, and has a tidy public beach and a marina where fishing and boating excursions are available. And it's all just tacky enough to be for real.

The other side of the resort is a 10-minute drive to the north at Ixtapa (icks-TAH-pah). It has five new hotels (and at least one other under construction), a fine beach, lighted tennis courts at each hotel, an outstanding new golf course and a new shopping center so elegantly designed that it does not look like a shopping center. Except for a few new homes bordering the golf course, that is all there is at Ixtapa, aside from beautiful scenery and nice, warm weather.

The weather might be the only significant drawback: Even in February, during the high season, it is pretty hot and humid, and many visitors find it just too warm to engage in sports during the middle of the day. An early tee-off at the golf course or an early-morning or after-dark tennis game are well advised. The pool or the ocean awaits. The breakers can be rough, but they're great for body surfing.

The golf course at Ixtapa is one of the prime features of the resort. It has to be one of the outstanding courses in Mexico, and some golfers believe it is better than the course at Cancun. Another indicator is that the president of Mexico goes to Imtapa to play golf. Called Club de Golf Palma Real, the course is open to guests of all the hotels there. It is an 18-hole, par-72 Robert Trent Jones layout that measures 6,408 yards from the regular men's tees. Like all RTJ courses, it is markedly longer and more difficult from the championship tees. About the only significant problem is the bunkers, which contain heavy, thick sand typical of a municipal course.