THE ALHAMBRA

The road up from the belly of the city to the main gate of the Alhambra is steep and narrow and bordered with old English elms, a reminder that Wellington was here during the Napoleonic wars. He found the Alhambra in ruins, with laundry hanging out the windows, squatters cooking meals over open fires, fountains choked with weeds, and dogs and pigs wandering around.

Washington Irving, who came a little later, describes these scenes in ''Tales of the Alhambra.'' His romantic imagination invested them with philosophic meaning; he relished the contrast between poverty and former splendor. For this had been the proudest part of the Moorish empire in Spain.

Moorish, Spanish, and Gypsy, Granada is exotic even for Spain. It is a city of extremes: violence and languor, harshness and beauty. The Alhambra is a perfect symbol of these opposites.

The curator told us, ''If you want to live lucky, live hidden.'' The exterior of the Alhambra - of grim, reddish stone - towers over the city like a fortress. But inside it is pure luxe, so exquisite that it seems not to belong to this world.

The secrets of the Alhambra must be studied slowly; they can tell us much of Moorish life. Washington Irving knew this, and he moved right in with the squatters, found himself a corner apartment, rebuilt some of the walls, and began writing down the stories told to him by these people, one of whom described himself as ''a true son of the Alhambra.''

It is a kind of paradise. Being so high above the city, it is host to cool breezes from the Sierra Nevada mountains while Granada, 100 degrees F. in the summer sun, bakes beneath it.

Water, brought from the mountains by ingenious methods of engineering, is very precious. Displayed like jewelry, it flows through marble and tile conduits , spouts out of fountains, lies still in silver pools. Even the sound of water is deliberate and carefully orchestrated.

In the Alhambra, as in a Bedouin camp, most of the rooms open onto a center court, the source of water and shade, where nightingales sing, jasmine scents the air, and flowers bloom. It is a haven of coolness in the hot fields of Andalusia.

The Alhambra was a conspiracy of peace and quiet in a world of danger and deceit. After 800 years of Arab rule little remained in Spain of that vast culture of laws, science, literature, and architecture, but the best of these is the Alhambra.

It should be read like a book. In fact, that is what its architects intended. Interior walls, a mixture of plaster, alabaster, and marble dust, were soft enough to write on when wet. Covered with designs, those decorative walls are really Persian letters; inscriptions from the Koran; anecdotes from history; edicts of government; and poems of birds, stars, beautiful women - and water.

The Moorish passion for design is everywhere apparent. Originally brilliant colors were used on these walls, which are now faded - blues and greens in private areas, reds and gold in official reception rooms. Walls were inlaid with cedar, which was in turn inlaid with ivory. In the Hall of the Ambassadors, the entire ceiling is of carved cedar. Inscriptions on the walls, which are 60 feet high, represent the seven different levels of the Muslim paradise.

Slender columns proliferate like clusters of palm trees in a desert oasis, as in the Court of Lions, named for crouching lions that hold up a huge basin of water. The small gallery off this court has a ceiling carved like stalactites and a star-shape cupola. In this exquisite chamber 36 members of one family, the Albencerrajes, were beheaded.

The $2 entrance ticket to the Alhambra has a map on the back with red arrows indicating best routes to follow through these labyrinths. The route leads through the Mexuar, or court of justice, where many varieties of wood and tile decoration typical of Granada can be seen. Walk through the Court of Myrtle Trees with its long reflecting pool; the Hall of Two Sisters, which was the harem; the Hall of the Ambassadors; the Daraxa Garden; and the Window Grill Court; then down to the baths.

Small openings in the ceiling of the baths let in mysterious, muted light by day and reveal the stars by night. A hollow floor was heated by fires underneath , as in Roman baths. Dancers entertained sultans and their visitors here while blind eunuchs played music from balconies above. The curator suggested that ''more business was transacted in the baths than in the halls; indeed, this court was known for statesmanship.''

The Partal Gardens east of the palace are terraced to the embankment that leads down to the Darro River. Arched windows in the 14th-century Lady Tower frame blue-green views of distant hills as in miniature Persian paintings.

The oldest part of the Alhambra is the Alcazaba. From the top of its 9 th-century watch tower is a 360-degree panorama of the summer palace a quarter of a mile distant across the river; Sacromonte, the hill where gypsies live; the city of Granada; and the snow-capped Sierra Nevadas.

The gardens of the summer palace (Generalife) are considered among Europe's greatest. Pools, fountains, columns, and arches framing distant views create a sense of peace and harmony. Oleander, myrtle, and persimmon trees complement yew and boxwood hedges; roses, lilies, wisteria, and bougainvillea add color. The gardens are modern, not Arab. Close by is the monastery of San Francisco, where Ferdinand and Isabella were first buried.

One visit is not enough to see the Alhambra, especially in groups with tour guides shuffling people through. Go back a second time, perhaps in the evening when few people are there. Even better, go on a moonlit night for an unrivaled sense of romance. Sometimes snatches of flamenco music float up from parties on the river below. (Evening hours are 10 to midnight May to September, 8 to 10 in winter. Daytime hours are 9 to 7 June to September, 10 to 6 in winter.)

Adjacent to the Alhambra is the Palace of Charles V, one of the most important Renaissance buildings in Spain, built by Machuca, a student of Michelangelo. Its monumental quality - a huge open circle within a square - is a stunning contrast to the delicate lines of the Alhambra. Acoustics are so fine that every year in late June-early July an international festival of music and dance is held here. It houses the Hispano-Moorish Museum, which has objects used in the Alcazar, including a masterpiece, the blue amphora. The Fine Arts Museum, with paintings from the 16th to the 18th centuries, is also here.

Granada itself is built on three hills; the Alhambra and the Sacromonte occupy two of them. The third, facing the Alhambra, is called Albaicin. From the plaza of the Church of Saint Nicholas is one of the finest views in Granada - sunset over the Alhambra. Site of the first Moorish fortress, this became the Arab quarter after the reconquest. White-walled houses, narrow alleys, and enclosed gardens are very pretty.

The oldest part of Granada is the hill of Sacromonte. Riddled with caves even today, it is said to have been lived in by early Christian fugitives. (The word Granada actually means mountain cave.) Gypsies now live in these caves, and gypsy customs flourish here. Flamenco singing and dancing is common, but the best dancers go to the hotels as entertainers. (Visitors are usually advised not to go here alone or with money.)

Ferdinand and Isabella were not happy in the Alhambra with its echoes of the Arabian nights, the harem apartments, and the sybaritic baths. They moved into the monastery of San Francisco, and they built a chapel on top of the gypsy hill , which they named Sacromonte. They decided to build a monument on the site of their victory over the Moors (1492) in the part of Granada known as the Alcaiceria. It was the medieval silk market; now its narrow, winding streets are crammed with small souvenir and craft shops.

The monument became the Royal Chapel; it is the only Gothic building in Granada. Completed by Charles V in 1521, it is alive with Isabeline-type work - wrought-iron grills, ribbed vaulting, monograms of initials and coat of arms, and an ironwork screen by the master Bartolome.

The dank splendor of the Royal Chapel is dominated by the mausoleums of the Roman Catholic monarchs, but they are raised so high it is impossible to view their figures on top. Next to them are Juana la Loca, their daughter, and her husband, Philip. They are a formidable group.

A pleasant surprise are the fine Flemish, Italian, and Spanish paintings in the sacristy, known as the queen's collection. It includes work by Perugino, Boets, Memling and Botticelli, as well as two parts of a triptych by Roger van der Weyden. (The third part is in the Metropolitan in New York.)

Next to the Royal Chapel is the cathedral, completed much later. It is essentially baroque, with an unusual rotunda; the sacristy is of cedar inlaid with mother-of-pearl and silver. Practical details

On the grounds of the Alhambra is the Parador Nacional de San Francisco, quite small, with reservations required months ahead ($50 double). In the US, write Marketing Ahead, 515 Madison Avene, New York, N.Y. 10022, or telephone ( 212) 793-5000 for reservations. Another small hotel on the grounds is the Hostal America, open March to October ($25). The Washington Irving Hotel ($40) is not far away, but the Alhambra Palace, four star, near the gate, is a large, old-fashioned Victorian hotel now legendary, with delightful terraces overlooking the city ($50).

Classic Spanish food is served at the Parador San Francisco. The Sevilla at Oficios 14 and Los Mariscos at Escudo Carmen 25 are also recommended. Dinner generally costs about $10 complete.

From Madrid, by car, it is 210 miles on Highway IV (50 miles more on good secondary roads). There are also train and bus connections. By air, fly to Malaga on the Costa del Sol (one hour), then drive about 75 miles northeast.

For more information write or call the Spanish National Tourist Office at 655 Fifth Avenue, New York, N.Y. 10022, (212) 759-8822).