Edward Baxter Marsh Sr., 85, who wrote landmark decisions affecting the natural gas and petroleum industries during his 26-year career as an examiner with the old Federal Power Commission, died Wednesday at the Washington Hospital Center after a heart attack.

Mr. Marsh joined the FPC, now part of the Department of Energy, in 1938 as a hearing examiner. In 1953, he was appointed chief hearing examiner, a position he held until retiring in 1964.

Among the decisions he wrote during that time are two which stand as landmark cases. One, involving the Hope Natural Gas Co., set the basic principle for modern utility rate-making.

The other, involving the Phillips Petroleum Co., established the jurisdiction of the FPC over the production of natural gas.

Mr. Marsh received a distinguished service award for his work with the commission.

Born in Salisbury, N.C., he attended the University of North Carolina at Chapel Hill and its law school and earned a law degree from Valparaiso University in Indiana.

He practiced law in Gary, Ind., and in Palm Beach, Fla., before moving to the Washington area.

Mr. Marsh served in the Army during World War I.

He lived in Bethesda and was active in St. John's Episcopal Church in Chevy Chase. He also was active as a volunteer at the Norwood School in Bethesda, which was founded by his wife of 50 years, Frances Brandis Marsh.

He was a member of the Temple-Noyes-Cathedral Lodge No. 32 of the Masons.

Besides his wife, of Bethesda, survivors include two sons, Dr. Edward B. II, of Ipswich, Mass., and Dr. Henry B., of Chevy Chase; a sister, Rebekah M. Stokes of Baltimore; a brother, Dr. Frank B., of Salisbury; a half-sister, Margaret M. Herman of Greensboro, N.C., and four grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Norwood School in Bethesda, or to St. Alban's School in Washington.