MOST FIRE INVESTIGATORS HAVE COME TO RECOGNIZE THREE CATEGORIES OF ARSONISTS: (1) THE PATHOLOGICAL FIRE-SETTER, (2) THE GENERAL ARSONISTS (INCLUDING THOSE WHO SET FIRES FOR PROFIT OR REVENGE), AND (3) THE JUVENILE FIRE-SETTER. ARSONIST PRACTICE THE CRAFT FOR MANY REASONS--TO REALIZE A PROFIT, TO FURTHER A CAUSE OR OBTAIN A GOAL, TO CONCEAL ANOTHER CRIME, OR SIMPLY BECAUSE OF SOME MENTAL ILLNESS OR IMBALANCE. STUDIES HAVE SHOWN THAT THE MAJOR MOTIVATION IS PROFIT, ALTHOUGH IN SOME LOCALES, NEW YORK FOR EXAMPLE, REVENGE HAS BEEN ESTIMATED AS THE MOTIVATION FOR AT LEAST 50 PERCENT OF SOME 8,000 CASES THE CITY FIRE DEPARTMENT HAS PROCESSED. WHILE ARSON HAS BEEN ON THE INCREASE IN MOST MAJOR CITIES, BOSTON, MASS., HAS EVIDENCED A DECLINE, DUE IN PART, TO THE WIDELY PUBLICIZED TRIALS OF 33 MEMBERS OF AN ORGANIZED ARSON RING. SEATTLE, WASH., HAS ALSO REPORTED A MODEST DECLINE AS THE RESULT OF AN ALL-OUT EFFORT BY INSURANCE ORGANIZATIONS AND PUBLIC SAFETY AGENCIES TO HELP EACH OTHER AND TO SEEK COMMUNITY HELP. THE FIRST STEP IN SEATTLE'S FIGHT AGAINST ARSON INVOLVED THE ESTABLISHMENT OF AN ARSON UNIT, UNDER THE JURISDICTION OF THE FIRE DEPARTMENT. THE WASHINGTON INSURANCE COUNCIL SUBSEQUENTLY SPONSORED A $20,000 MASS-MEDIA CAMPAIGN PROMOTING THE USE OF THE ARSON UNIT'S HOTLINE. TO FURTHER ENCOURAGE WITNESSES TO COME FORWARD, THE COUNCIL ESTABLISHED A $5,000 REWARD FUND AND SUPPLIED SIGNS TO BE POSTED AT ARSON SITES. THE SIGNS INFORM THE PUBLIC THAT THE FIRE WAS CAUSED BY ARSON AND MENTION THE NAME OF A CONTACT AT THE FIRE DEPARTMENT AS WELL AS THE EXISTENCE OF THE REWARD FUND. PHOTOS ARE INCLUDED. (KBL)