EUGENE, Ore. (AP) _ An incendiary device heavily damaged a section of an Internal Revenue Office building three days after a U.S. Army Reserve Center was firebombed, authorities said.

Investigators said ''peace movement'' literature was found near the damaged office of the Examination Division, which conducts tax audits of businesses, but said it was premature to link the Sunday fire to anti-war activists.

''It is an arson,'' said police Sgt. Becky Hanson. ''We have determined an incendiary device started the fire.''

She said the fire, which caused an estimated $30,000 in damage, bore similarities to Thursday's attack, when Molotov cocktails were tossed into the reserve center, causing some $20,000 in damage.

Several anti-war demonstrators have taken place in Eugene, 110 miles south of Portland, and protesters have maintained a vigil outside the Federal Building since the outbreak of war in the Persian Gulf last week.

Peace activists denounced the fires. ''These are outrageous acts of individual violence, and we have nothing at all to do with them,'' said Randy Prince, a spokesman for Eugene Peaceworks.

Dwight Sparlin, supervisor of the IRS Criminal Investigation Division, declined to elaborate on the nature of the literature found near the fire.

Peaceworks spokesman Thom Alberti said the literature may have been left by someone who wants to discredit the anti-war movement.