"INDIAN HEAD, Md., Dec. 19 (AP) - Racial animosity and revenge are among the possible motives in the arson fires in a subdivision in southern Maryland on Dec. 6, a spokesman for federal investigators said Sunday. Four men have been charged with arson in the fires, which destroyed 10 houses and partly burned 16 others, causing $10 million in damage. No one was hurt; many of the houses were still under construction. A federal law enforcement official speaking on the condition of anonymity said two of the four men in custody made racial statements to investigators during questioning. The men are white, and many of the families moving into the development are black.