MALIBU,CALIF. -- The J. Paul Getty Museum has purchased one of the key works of modern painting, James Ensor's huge "Entry of Christ Into Brussels" (1888).

The purchase, announced Friday by John Walsh Jr., the museum's director, contradicts the Getty's policy of avoiding the acquisition of modern works of art, but it brings one of the most important precursors of surrealist and expressionist painting to rest in Southern California.

Walsh called the acquisition "the museum's most important painting."

The Getty bought the 1888 work from a private foundation in Liechtenstein; it had been on loan to the Kunsthalle in Zurich since 1983. As usual, the museum declined to disclose the price, and even sources familiar with the art market found estimates difficult because of the Belgian artist's highly individual position and the virtually legendary status of the painting.

"It has to be in the millions," said one puzzled authority, "but even guesstimating closer than that would be irresponsible."

Ensor (1860-1949) is hardly a household name to the general American public, but he is revered in Europe, especially in Belgium, where he is bracketed with such precursors of modern art as Vincent van Gogh and Edvard Munch in the development of an intensely personal painting style that carries the artist's feelings through high-key color and distorted form and space.

Ensor's painting is a seething mass of masked figures disappearing into a deep funnel of space with a small image of Christ (who has Ensor's face) almost lost in their midst. According to one account, he painted it as a satire of the power of the church, the rise of mass culture and its mindless conformity.

At about 14 feet wide, it was Ensor's most ambitious work. It was derided by contemporaries, and some critics feel he overreached himself in it, but no one disputes its historical importance.

The painting will be cleaned before being placed on public view, probably in "a few months," said Laurie Starr, the Getty's public relations director