ZURICH, Switzerland (AP) _ A West German arrested after a 17th century painting by Peter Paul Rubens was destroyed by fire said Friday he had burned it ''to protest environmental pollution,'' police reported. The painting was valued at $1.9 million.

The man, whose identity was withheld, was jailed on a provisional charge of arson and grave destruction of property, said police spokesman Hans Huber.

''He said he did it to protest environmental pollution,'' Huber said. ''He also carried a written note with about these words.''

The attack, during afternoon visiting hours at the Kunsthaus Museum, destroyed the Flemish painter's 1628 portrait of Spanish King Philip IV. A guard discovered the fire after seeing smoke emerging from the first floor room where the painting was on exhibit.

Efforts to stop the blaze with a fire extinguisher were unsuccessful. Huber said the canvas, measuring 24.5 inches by 31 inches, was reduced to ashes, leaving only the frame.

The suspect, who remained silent for almost 24 hours, admitted the attack after samples of his clothing showed he had been in contact with ''certain chemicals,'' Huber said.

Kunsthaus curator Guido Magnaguagno told The Associated Press that the fire was started with a paste commonly used to ignite charcoal in a grill.

''The destruction of this portrait comes as a shock for museum officials throughout the world,'' he said. ''Never before has an irreplaceable work of art been destroyed in such a way.''

The painting had been on permanent loan to the museum from a private foundation administering the collection of the late Professor Leopold Ruzicka, the Yugoslavia-born Swiss winner of the 1939 Chemistry Nobel Prize.

Last Jan. 10, another Rubens - a painting of the Greek mythological couple of Orpheus and Eurydice - was cut out of its frame and stolen from the museum. It has not been recovered.

After that theft, some Zurich politicians complained about inadequate security measures at the museum, which has a collection ranging from classical to modern.

Rubens, who lived from 1577 to 1640, painted more than 100 works for the Spanish court. He went to Spain in 1928 on a diplomatic mission, became acquainted with Spanish master Diego Velasquez during his nine months in Madrid and did portraits of the royal family.

Philip IV was born in 1605 and was king of Spain from 1621 until his death in 1665.