TEHRAN (REUTERS).- Artists like Monet, Picasso and Warhol were considered revolutionary in their day, but their works were not much appreciated by the leaders of Iran's Islamic revolution and many were kept out of view for decades.

Now, one of the greatest collections of contemporary Western art -- put together under a Western-leaning monarchy in pre-revolutionary Iran -- is open to the public, with some works on display for the first time in more than 30 years.

In the Islamic Republic, where the United States is considered the "great Satan" and its decadent music and movies are considered the products of a Godless society, the art exhibition is full of cultural contradictions.

The first paintings visitors to the Tehran Museum of Contemporary Art see are of Ayatollah Ruhollah Khomeini, the founder of the Islamic Republic, and his successor as supreme leader, Ayatollah Ali Khamenei -- portraits that are compulsory features of all public buildings.

Below their austere gaze, a winding staircase leads down to what looks like an empty black plinth, but on closer inspection proves to be a modern art installation -- an open vat of crude oil -- the substance that paid for Iran's priceless collection.

The galleries of the stark concrete museum -- built especially to house the collection during the latter years of Shah Mohammad Reza Pahlavi's reign -- are works by pretty much every major Western artist of the late 19th and 20th centuries.

"Without exaggerating, Tehran's contemporary art museum has one the most important treasuries of artistic works in the world," said Ehsan Aghaie, executive manager of the exhibition which runs throughout the summer.

Past the French impressionists, the Van Gogh lithographs and the self-portrait of Edvard Munch, sculptures by Pablo Picasso, Henry Moore and Alberto Giacometti litter the hallways.

Aghaie says the collection has been valued at more than $2.5 billion. Its most prized piece, "Mural on Indian Red Ground," a violent spatter of color painted by Jackson Pollack in 1950, fills half a wall.

The challenging works draw a crowd. "Iran is not separate from global community. (Modern art) is widely welcomed by people and when these works are exhibited the number of visitors rises dramatically," Aghaie says.

COCKTAIL
Women in chadors gaze at plain black canvasses with the same looks of incomprehension that similar "post-minimal" works inspire in visitors to galleries in the West.

A Picasso painting of the artist and his model is abstract enough not to risk offending prudish sensibilities.

A colorful meter-high bronze by Roy Lichtenstein looks like a giant glass filled with a fruity cocktail -- not a common sight in the Islamic Republic where alcohol is banned.

Next to it, one of the pop artist's cartoon-like paintings shows a fighter pilot picking off enemy planes.

The fantasy image is a world away from the grim eight-year Iran-Iraq war which followed the 1979 revolution and put such modern, Western art out of favor and into the storage vaults.

Portrayals of Iranian military might -- like the murals which still decorate Tehran's walls -- were the kind of art in vogue during the war with Saddam Hussein's Iraq, backed by many of the Western countries which had produced the art.

Aghaie is keen to dispel the idea that Iran ever banished its Western art treasures, even though they were kept out of the public eye for years.

"Perhaps during war time, countries try to keep the epic sprit of their nations high. Therefore, there is more appetite for that kind of art," Aghaie said. "But it does not mean that there was no appetite for these art works."

"Even in the West, after World War II, war elements were more evident in artists' works, and Iran is not an exception.

"But this kind of art has never been rejected and Iranian people and authorities always liked them, that is why they are safe and sound and now you can see them," he said.

The collection, which contains around 4,000 pieces, was always stored in good conditions, even when it was kept out of sight, Aghaie says.

Iran's authorities have no desire to suppress the collection, he says, but there is simply no room to display them all at once. In future the museum may mount theme-based exhibitions, rotating the collection through various schools of art.

Leaving the museum, visitors once again pass the oil installation which fills the atrium with a mild smell of petroleum that employees at the gallery no longer notice, back into the polluted real-world air of Tehran where Iran's biggest export is put to a more conventional use.

(Editing by Paul Casciato)