The Scholastic Corporation announced yesterday that Barbara A.
Marcus, who built its children's book business into an industry
powerhouse, was leaving and would be succeeded by Lisa Holton,
the publisher of the children's books division at the Walt
Disney Company.  But a spokesman for Disney's consumer product
division, Gary Foster, said last night that Disney was surprised
by Ms. Holton's appointment at the rival publishing house,
because she ''has not been released from her employment
agreement.''  Mr. Foster said Disney would try to block the
move.  As executive vice president of Scholastic and president
of children's book publishing and distribution, Ms. Marcus
oversaw the publication in the United States of the five Harry
Potter novels published so far.  Ms. Holton, who is also a
senior vice president of Hyperion, the Disney books unit, said
yesterday that she would start at Scholastic on May 23,
overlapping Ms. Marcus by about two months.  ''Scholastic is the
only company that reaches out to children di