Patricia A. Dean, 55, a partner with the Arnold & Porter law firm in Washington, died of cancer Oct. 27 at Virginia Hospital Center. She lived in Arlington.

Ms. Dean, a Washington native, graduated from J.E.B. Stuart High School in Falls Church. She received a bachelor's degree from Georgetown University and in 1981 received a law degree from there.

She was a deputy clerk of the U.S. Supreme Court from 1978 to 1981, the first woman to serve in that position in the court's 200-year history.

She clerked for Judge Edward A. Tamm of the U.S. Court of Appeals for the D.C. Circuit in 1981 and 1982, then for Supreme Court Justice Byron R. White in 1982 and 1983. She was an associate at Hughes, Hubbard & Reed from 1983 to 1988, then moved to Arnold & Porter, where she became a partner who specialized in litigation, focusing on securities fraud.

Ms. Dean worked on cases involving Fen-Phen, the weight-loss drug withdrawn from the market in 1997 after some consumers developed heart disease. She also represented clients in constitutional cases involving the issue of aid to religious educational institutions.

Ms. Dean was a trustee of the Loyola Foundation, a Catholic charitable organization, for the past three years.

A brother, Lawrence E. Dean, died in 1973, and her mother, Delores M. Dean, died in 1987.

Survivors include her father, Paul R. Dean of Fairfax, who was dean of the Georgetown University Law Center for 15 years; and seven siblings, Mary E. Dean of Milford, Del., John E. Dean of McLean, Paul R. Dean Jr. of Vienna, William J. Dean of Arlington, Delores A. Dean of Annandale, Teresa M. McCabe of Arlington and Brian D. Dean of Chantilly.