Cruising along Mexico's Baja peninsula

The blue-green surface of the waters around Baja California teems with activity in the winter and spring. For instance, you can see tiny pelagic crabs, which ride on a strange oceanic elevator system. These crustaceans often swarm in deeper waters, but sometimes they are pursued by sharks and fishes to the warm sea surface. Here - where they can be admired by well-wishers - they ride the currents, flailing their tiny pincers, and sparkling bright red in the afternoon sun.

Gray whales have a more constitutional commitment to the ocean surface; these global migrants have a difficult assignment as air-breathing creatures living an entirely aquatic life. Habitual travelers, they annually swim almost 10,000 miles from the Bering Sea to their breeding and birthing waters here in sequestered lagoons along the Pacific shore of Baja California.

Tourists watch whales all along the California coast. But this year, joining the whale for the end of its journey, is a seasonal migrant of another sort. Bound also for Baja's Pacific coast and then on into the Gulf of California (Sea of Cortez) and its unusual flora and fauna is the stately 143-foot Pacific Northwest Explorer.

For this season, the Baja California Circumnavigated tour will be offered every two weeks until the end of March. Next year, Special Expeditions Inc. (an associate company of Lindblad Travel) plans to extend this program well into the spring.

The Baja California peninsula is relatively uninhabitated, and passengers are dependent for companionship and entertainment on the ship. The highlights are the daily shore excursions led by the staff of trained naturalists and committed environmentalists. Trips are preceded by lectures on the flora and fauna of the area. For the first cruise of 1983, Special Expeditions provided for the edification of just 60 passengers a total of six such experts, including a Canadian representative to the International Whaling Commission, several champions of the Mexican green and ridley turtles, and researchers on salt-tolerant agricultural plants.

At the helm of the ship is Capt. Robert Hempstead, a philosophical, certified master of any-size ship who has taken over the Explorer's bridge for the adventure of cruising with whales.

Just off of San Diego, in our plunge southward toward Mexico's Los Coronados islands, we came upon this year's vanguard company of grays. Of course, every trip will be different, but our first close view of the whales was of three spouts directly off our port bow. It was a courting group, perhaps - two males and a female dallying at the international border. Off the other rail, we watched as, graceful and controlled, two whales breached the water beside us, their exhalation an audible explosion, their di-Oo ive saw-toothed vertebrae slicing the air on their graceful downstroke before they disappeared.

These whales were bound for the Baja shore and so were we. But first we headed south for a day and a night to the San Benitos islands, where portly and vociferous pinnipeds loll and squabble, mate and sleep.

The pinnipeds are a class of sleek marine mammals that includes both the gargantuan elephant seal and his voluble cousin, the California sea lion. That morning, launched at the big ship's fantail, comical motorized rubber rafts called Humbers ferried us ashore. We careened around a small cove's swirls and eddies to the west island.

Squeals, barks, snorts, and cries were not the only instruments elephant-seal performers used to send messages from one corner of their sandy beach passageway to another. Huge males were broadcasting their views on topics of the hour with terrible sounds like the revving of Mack trucks and punctuated hollow croaks like the sound of drums falling downstairs.

All the commotion was certainly not for our benefit. As we looked down over the snoozing masses - clumped together, sprawled one on top of the other - even the pups of the year, some not yet two weeks old, were nonchalant in our presence.

Elephant seals came close to extinction in the late-19th century. And once whalers had thinned the oceans of the whale, they moved on to its rotund lesser relatives. Yet from one colony protected since 1922 on an island a bit farther west off of Baja, the entire species has made an astounding comeback.

After cruising southeast overnight, we arrived at the Laguna San Ignacio, only to find that we were ahead of all but the swiftest of the gray whales, who were late this year. (Because our Special Expeditions trip was given a new classification by the government, that of ''ecological tourism,'' we were able to approach the lagoon, which is off-limits to all but permit holders.)

By now, this lagoon and the two other Baja whale nurseries, Laguna Ojo de Liebre and Bahia Magdalena, must be full of ponderous grays, first the pregnant females - and a few mothers with calves born en route - later, the courting groups and other stragglers. While we were there, though, surf scoters kept us company, darting in silhouetted family groups, the wind leaking with an odd whistling sound off the backs of their swift wings.

For the whales' protection, the Mexican government has set strict policies for the use of these unique habitats. Laguna Ojo de Liebre is off-limits to maritime tourists; Laguna San Ignacio, once again, is open on a limited basis only; Bahia Magdalena, encompassing a small commercial port, welcomes all.

Chaubascom weather - monstrous cloud formations in yellows, peaches, and blues lashed by tongues of light - caught us at Bahia Magdalena. Haze across the water made the islands and the distant shore appear to float on a shimmering layer of air.

But these dramatic clouds were not the only unusual color to be seen; it was obvious that some days earlier a tropical storm had broken into this normally arid zone. The desert sandbar, which separated the bay from a hard-packed surf beach on the Pacific side, was a garden of fragrant botanical delights. The spurge, the evening primrose, and sweet purple verbena had waited perhaps a year for an unlikely shower that would bring forth their choice and tiny flowers.

Another overnight sail brought us to Cabo San Lucas. The state of civilization of this Land's End, at the far tip of the Baja peninsula, is changing right now with much clamoring of jackhammers. This erstwhile little fishing settlement seems uncertain at the moment whether to call itself a village or a resort. The several luxury hotels and condos built on stilts into the hillside seem out of keeping with the tiny huts and cheap curio shops below. Although the town is at the most remote end of Baja's newly paved 800 miles of highway, the small airport just outside makes Cabo just a convenient hop from Los Angeles.

The cape itself is a wild sculpture garden of craggy pinnacles. Here stand the symbolic ramparts of stone that mark the point where the Pacific yields to the Gulf of California, a sea lesser in scope but yet full of mystery and suggestive beauty. The narrow tip of Baja, bashed over the millennia by fierce currents, has broken here into the tall Friar's Rocks, jagged beige bulwarks with crusty bridges and spires of stone.

As we began our foray into the Gulf of California, hugging the peninsula's eastern face, which is broken by black and molasses streaks from ancient lava flows, we sighted dorsal fins breaking the choppy waves. A pod of maybe 60 often-airborne dolphins sailed past our ship; a few shifted course to pay us homage with sporty leaps.

Off La Paz, the shore capital of Baja California Sur, two sleek, almost green-black humpback whales surprised us with a flourish of flukes. These great vocalizers among whales produce different ingenious though syntaxless song sequences in each of their regional habitats. The Baja humpbacks, though, share a tune with their Hawaiian relatives.

If the Beagle had strayed off course and into the Gulf of California, Darwin would not have been ungratified. As in the Galapagos, strange endemic species of plants and animals mark each of these islands with a unique signature.

We visited some seven or eight of these islands, as well as the mainland, to see their unique fauna. However, the famous rattleless rattlesnake on one of our next stops, Isla Santa Catalina, thoughtfully kept out of our path. A more welcome sight, up a verdant desert arroyo, was Costa's humming bird, which dipped its pale-amethyst head into the red flowers of a rare mistletoe in bloom.

Isla Danzante, a dry little island heaped with rocks like brick and mortar, could almost be mistaken for a giant prehistoric reptile soaking in the vast blue puddle of the gulf. From its spiney back, we watched at least 5,000 eared grebes and northern phalaropes paddling in a dense aggregation, like a solid floating barge in the straits between the island and the mainland. These winged divers were feeding on schools of scrumptuous anchovies, driven to the surface, perhaps, by our cetaceous friends.

An equally gripping zoological world was just one step off the beach for those equipped with mask and fins. Two hundred sleek, silvery jacks were moving in strict underwater ranks, clearly obedient to a single command. Tiny, ubiquitous yellow- and black-striped sergeant major fish kept company with great box-shaped king angelfish, black with incandescent purple trim and gaudy orange tails. The spotted Pacific Creole fish traveled alone, while just below the surface skinny, transparent needlefish wiggled and threaded their way through the bubbles churned up by the turgid surf.

The end of the trip was its climax: the island of San Pedro Martir, famed above all others in this exotic zone. Like a strange tall iceberg out of place in a mild and burgeoning sea, the volcanic San Pedro Martir stands 30 miles offshore, where tidal currents buck the prevailing winds.

The island is a frosted spectacle, covered by white guano from the generations of seabirds who've made this square-mile island their mid-gulf outpost. Long ago, convicts were exiled here to mine the guano for fertilizer. Though probably very little could have cheered workers at such a dismal task, the vocal and affectionate sea lions that congregate on these shores by the thousands probably did their best.

We took our ultimate Humber cruise in and around the sea caves at the base of the island cliffs. The juvenile sea lions, yearlings and two-year-olds, dove with acrobatic swoops from their shore-rock stations to the side of our idling craft. The sea boiled with the bobbing heads of pups who left their phlegmatic though talkative parents piled up in sociable groups on the rocks. Unafraid, these small creatures wove graceful circles around the snorkelers in our company.

That night, as the warm air drifted off the island, we watched hundreds of thousands of sea birds - Heermann's gulls, brown- and blue-footed boobies - stream in from all points on the horizon after a day of fishing on the gulf. The screams and barks of our sea companions for the day echoed in the deep sea-cave chambers at the water line. We felt that, with the eerie high and low tones of this aquatic chorus, we were being delivered an injunction to remember all of the creatures of Baja who had trusted us and approached us with such inimitable grace. Practical details: Trips begin alternately at San Diego and at Bahia de Los Angeles on the Gulf of California. The Pacific Northwest Explorer chartered by Special Expeditions Inc. carries a maximum of 66 passengers in 39 outside cabins of various sizes. Meals served on board, American-style, at one sitting offer local produce and seafood. The trip costs, which include all meals and shore arrangements for the two-week period, range from $2,650 (for lower-deck double cabins) to $3,680 a person (for bridge deck or upper-deck name cabins). For further information contact Special Expeditions Inc., 133 East 55th Street, New York, N.Y. 10022.