LOS ANGELES, AUG. 3 -- A federal judge today approved a reapportionment plan for the Board of Supervisors that dramatically realigns political representation for many of Los Angeles County's 8.5 million residents.

U.S. District Judge David V. Kenyon approved new district boundaries drawn by civil rights groups that are designed to help a Hispanic win a seat on the powerful five-member board. The new map threatens to end a decade of conservative control of the county's governing body.

In a three-paragraph order, Kenyon also canceled the November runoff between Sarah Flores and Gregory O'Brien for the 1st District seat being vacated by retiring Supervisor Pete Schabarum. The judge ordered a new primary Nov. 6 in the redrawn 1st District, which under the court-ordered plan is now predominantly Hispanic.

The district was mapped by a University of California, Los Angeles, professor of urban planning on behalf of the Mexican American Legal Defense and Education Fund and the American Civil Liberties Union, plaintiffs in the historic voting rights case against Los Angeles County.

Kenyon turned to the plaintiffs' plans on Wednesday after he rejected a map by the board's conservative majority, calling it "insensitive" to blacks and Hispanics. Kenyon ruled June 4 that the five Anglo supervisors intentionally discriminated against the county's 3 million Hispanics when drawing district boundaries in 1981.

Hispanics make up one-third of the county population, but no Hispanic has served on the board since 1875. The county is appealing Kenyon's ruling.