Magnificent, overpowering: The Grand Canyon

''It is useless to try to describe the Grand Canyon,'' British author J. B. Priestley wrote. ''Those who have not seen it will not believe any possible description; and those who have seen it know that it cannot be painted in either pigments or words.''

Priestley canceled his ongoing reservations and stayed to savor the miracle: He had arrived, and there had been no anticlimax. ''Reality had gone to work to show me a thing or two. I thought I could imagine a better Grand Canyon, did I? Well, cried Reality, take a look at this - and - oh boy! - you ain't seen nothing yet.'' The canyon, he said, was ''enough in itself to clear a whole continent from the charge of dullness.''

Reality is still confounding visitors to the canyon, their credence taxed by its 1,000 square miles of crimson gorges, cataracts of light, eroded spurs, banded walls, purple abysses, and knobby promontories. To the early Spanish explorers the formations were larger than the tower at Seville; to Priestley they were ''ruined red cities,'' ''a perpendicular Assyria,'' and to Carl Sandburg ''elephants grappling gorillas in a death struggle.'' John Wesley Powell, the one-armed Civil War veteran who first navigated the Colorado River the length of the canyon in 1869, wrote of the ''ledges from which the gods might quarry mountains,'' the ''ten thousand strangely carved forms.''

Where, exactly, is the Grand Canyon? This might seem an idle, even an absurd, question, but when it was recently put to a group of 32 college freshmen, only seven knew the state.

Carved by the Colorado River, the canyon runs roughly east-west in northern Arizona, stretching 217 miles and ranging from 4 to 18 miles in width. It has an average depth of a mile and has five of North America's seven temperature zones. Autumn and spring are the ideal seasons to visit, but we did not find July too hot or crowded.

The first recorded viewing of it was in 1540, by Don Lopez de Cardenas, a captain in Coronado's expedition, although it had long been known to native Americans. One of the most inaccurate predictions in history was made in 1858 by Lt. Joseph C. Ives, an explorer who, not knowing of earlier expeditions, wrote, ''Ours has been the first, and doubtless will be the last, party of whites to visit this profitless locality.'' There are 3 million annual visitors now.

The South Rim, where 9 out of 10 visitors stay, is reached from Williams, Flagstaff, or Cameron; it has services at Grand Canyon Village. The North Rim, 214 miles away by road from the village, is reached from Jacob Lake. North Rim roads are usually closed by snow from late October to mid-May. Two drives extend from the village, one to Desert View (East Rim Drive) and one to Hermit's Rest (West Rim Drive). The latter is closed to private vehicles May through September , but free shuttle buses, 10 minutes apart, visit all viewpoints. Narrated scenic coach trips also go along each drive.

The usual ways to see the canyon are by foot, by mule, by air, and by water; any of these will greatly augment the view achieved from the rim alone.

Inner canyon camping is controlled by the National Park Service. Reservations should be made well ahead, specifying proposed dates, campgrounds and trails, and number of people. Groups are limited to 15; campgrounds to 2 nights; nights in the canyon to 7.

South Rim camping is at Mather Campground or Desert View Campground (both operated by the National Park Service) and at Trailer Village (operated by concession). Desert View is closed in winter. Camping is first-come, first-served except at Mather, which accepts summer reservations. There are private campgrounds on US 180 just outside the park.

North Rim camping is at North Rim Campground (Park Service) or, just outside the park boundary, at De Motte Campground or Jacob Lake Campground (operated by the US Forest Service).

Overnight hiking permits are required as a safety precaution and environmental safeguard. Day hike permits are unnecessary. Principal South Rim trails are the Bright Angel from Grand Canyon Village, the South Kaibab from Yaki Point, and the Hermit from Hermit's Rest. From the North Rim the North Kaibab Trail goes to the river. A level rim walk extends from Hermit's Rest to Mather Point. For seasoned hikers there are several wilderness trails. Hikers should carry two quarts of water per person per day and turn back when one-third of the proposed hiking time has elapsed (canyon bottom temperatures exceed 105 degrees in summer).

An easier way to descend is by mule. Each morning at 8 at the corral near Bright Angel Lodge, clusters of uneasy hatted riders and patient, roped mules eye one another. Eventually the groups intersect and all are mounted. In strings of five or six, the mules step adroitly down the narrow gravel trail. ''Pull his head out! Don't let him nibble the canyon wall!'' the guides shout. By the end of the day, unlikely as it seems, riders and mules evince an admirable unity and mutual affection. The day trip goes to Plateau Point (12 miles round trip).

Advance reservations for all mule trips are essential, but a waiting list is kept for cancellations. The trips are vigorous and limited to physically fit persons over age 12 and under 200 pounds.

At all hours white and yellow specks can be seen swooping and hovering against the canyon walls. These are the scenic planes and helicopters. Our helicopter had four passengers and one pilot; Madison Aviation picked us up at the hotel. The 30-minute ride was incredibly beautiful, like riding a dragonfly through a mammoth roseate rock garden, hurtling toward walls with undulating stripes of color, dipping toward the green-fringed river, and rising past pueblo cliff dwellings.

Flights are year-round and may be booked just outside the park. Reservations are not essential, but a minimum of three people is required. Scenic plane flights originate at the canyon, Phoenix, Ariz.; and Las Vegas, Nev.

The Park Service licenses 21 river-running concessionaires. From May to September they run river trips along the Colorado River through the Canyon lasting from 7 to 10 days (longer ones are available). The full trips begin at Lees Ferry and go to Diamond Creek or Pierce Ferry, Lake Mead.

Horseback and wagon rides are available at Apache Stables, Moqui Lodge, just outside the park boundary.

Few hotels today warrant the status of linchpins on a journey, worth any amount of time juggling to visit, but the El Tovar is in this category. It is the largest structure on the South Rim. ''More than a hotel; it is a little village devoted to the entertainment of travelers,'' wrote Fred Harvey of his flagship hotel in 1909. His guests might include ''a New York or Chicago banker, a Harvard professor, an Arizona ranchman, an English globetrotter, or a German savant.'' It is much the same today, except that ladies are no longer provided with their own balcony Lounging Room, the better to ''see without being seen.''

The 100-room hotel is a National Historic Landmark, opened in 1905 to accommodate travelers on the Santa Fe Railroad. It had electric lights, its own greenhouse and dairy, and first-class amenities. In the style of a lodge, with a cavernous lobby, stained rafters, and wildlife trophies mounted on timbered walls, it is a monument to a leisured era in which the literati from the Continent and this country explored the West in slow-paced luxury. Pullman sleepers pulled up to a siding just below the hotel.

Fred Harvey was a British-born hotel entrepreneur who specialized in creating Harvey Houses along the Atchison, Topeka & Santa Fe railway line. He recruited ''Harvey Girls,'' women ''from age 18 to 30, of good character, attractive and intelligent,'' as personnel at his lodges. Though it was forbidden, many married frontiersmen, and Will Rogers once remarked that Fred Harvey ''kept the West in food and wives.''

A new generation of ''Harvey Girls'' caters to guests at the El Tovar. They distribute carnations and mints as they turn down beds. The epitome of grace under pressure, they glide about the dining room in traditional black and white uniforms, serving with one hand carefully held behind the back. Never mind that the guests are almost always more casually dressed, less wholesome-looking, and often less patient; by the end of a meal their smiles and efficiency have soothed the thorniest disposition.

What better way to begin the day than with Eggs Benedict at 6:30, overlooking the misty canyon? It may be the country's last oasis of civility. It should be said that the dining room also has young waiters who are equally skilled. The cuisine is excellent; Chef Colon specializes in veal dishes.

Other National Park lodges on the South Rim include the rustic Bright Angel and the contemporary Thunderbird and Kachina lodges. The Motor Lodge (incorporating the Mushwhip Lodge) and the Yavapai are away from the rim but are within the village and are served by the shuttle buses.

North Rim lodging is at Grand Canyon Lodge, which has 213 cabin and motel units on pine-shaded grounds.

It will be a rare visitor who does not wander through some of the other structures at the village, such as the Hopi House, a replica of a Hopi pueblo dwelling selling Indian crafts, or Verkamp's Curios, built in 1905 and still operated by the Verkamp family as a concession selling souvenirs and crafts.

Lookout Studio, designed by Mary Jane Colter, was built by Fred Harvey in 1914 to sell photographic prints and books about the canyon. It competed with the Kolb Studio, owned by Ellsworth and Emery Kolb, constructed in 1904. Until his passing in 1976, Emery Kolb photographed mule riders descending the Bright Angel Trail; his studio is now owned by the National Park Service, which will probably adapt it for use as an interpretive center.

Other buildings of interest along the rim include the Watchtower at Desert View, which imitates the Indian Kiva or ceremonial chamber; the Yavapai Point Museum, with geological collections; the Visitor Center, with exhibits and dioramas; and the Tusayan Museum, which traces the development of early man at the canyon. The Tusayan Museum is 22 miles east of Grand Canyon Village on a short spur leading off East Rim Drive.

Don Marquis once wrote that publishing a book of poetry was like dropping a rose petal down the Grand Canyon and waiting for the echo. Playing cicerone to the canyon visitor is an equally unpromising task, for its full grandeur is at once so personal and so majestic it resists disclosure. At most one may offer a few impressions and suggestions with the hope of tempting the reluctant, encouraging the adventurous, and, not least, countering the skeptical. Practical information: Camping, South Rim: Mather: Mather Campground, Ticketron Reservations, Box 2715, San Francisco, Calif. 94126. Group: Box 129, Grand Canyon, Ariz. 86023. Camping, North Rim: Group: Group Reservations, North Rim, Grand Canyon, Ariz. 86023. Hiking: Backcountry Reservations Office, Box 129, Grand Canyon, Ariz. 86023; ( 602) 638-2474. Mule trips: One day, $40; two days, $137 ($235 for two sharing cabin). Reservation Department, Box 699, Grand Canyon, Ariz. 86023 (or Phoenix Convention and Visitors Bureau, 800-528-6149). Helicopters: Year-round; 30 minutes, $60. Madison Aviation; (602) 638-2688. Grand Canyon Helicopters; (602) 638-2419. Airlines: Grand Canyon Airlines (year-round from canyon; 45 minutes, $50). Scenic (from Las Vegas or Phoenix; nonstop tour, $105; ordinary trip, $131; 800- 634-6801). Republic (from Las Vegas or Phoenix; round trip, $136; 800-441-1414). Lodging, South Rim (prices are for standard double): El Tovar, $60; Bright Angel , $30; Thunderbird and Kachina, $58; Motor Lodge, $40; Yavapai, $50. Lodging, North Rim: Grand Canyon Lodge, $34; Grand Canyon Lodges, Grand Canyon, Ariz. 86023 (800-528-6149). River trips: One concessionaire, the Ft. Lee Company of Page, offers an 8-day trip from Lees Ferry to Temple Bar (Lake Mead) in a motorized boat for $795, May through September. Reserve 9 months ahead. For full list of companies, write Box 129, Grand Canyon, Ariz. 86023. Horseback rides: Grand Canyon Lodges, Grand Canyon, Ariz. 86023; (602) 638-2401.