Robert Ash, 86, a senior partner in the Washington law firm of Ash, Bauersfeld & Burton and the author of several books dealing with tax law, died of a cerebral hemorrhage Monday at Suburban Hospital. He lived in Bethesda.

Mr. Ash, a former Washington counsel for Prentice-Hall Inc., began his tax law practice here in 1918. He became senior partner of Ash, Bauersfeld & Burton in 1955.

He served on many American Bar Association committees and was the ABA tax counsel for 10 years, during which time he set up and secured a federal tax exemption for the association's Fund for Public Education.

From 1960-68, he was a member of the Advisory Committee on Appellate Rules, Committee on Rules of Practice and Procedure of the Judicial Conference of the U.S., which revised and modernized the appellate rules governing all federal courts.

In 1960, he published "Tax Problems Encountered in the General Practice of Law," which was distributed to all members of the American Bar Association by its Special Committee on the Economics of Law Practice. He also was the author of "Preparation and Trial of Tax Cases," which is used as a textbook by the Practicing Law Institute. His book, "How to Write a Tax Brief," now in its 24th edition, was originally published in 1926.

Mr. Ash was born in Buffalo, N.Y., and earned a law degree from George Washington University. The university's law school twice awarded him its Alumni Achievement Award, first in 1965, when he established the Robert Ash Law Student Assistance Fund at the university, and again in 1977.

He was a Fellow of the American Bar Foundation and a member of the American Law Institute, the American Judicature Society and the American and D.C. bar associations.

Mr. Ash was one of the founders and original directors of Potomac National Bank and a member of the Metropolitan Club, Burning Tree Club and the Chevy Chase Club. He was a former vestryman at St. Francis Episcopal Church in Potomac.

Survivors include his wife, the former Frances Luna, whom he married in 1926, and a daughter, Fanchon Ash Oleson, both of Bethesda, and four grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Robert Ash Law Student Assistance Fund, George Washington University School of Law, Washington, D.C. 20052.