Orvin L. Nelson, 56, an attorney with the Indian Claims Commission when he retired from the federal government in 1976, died Friday at his home in Annandale after a heart attack.

Mr. Nelson began his government service in World War II, when he served in both the Navy and the Army. After studying law in Saint Paul, Minn., he moved to the Washington area in 1951 and became a junior management assistant with the Civil Service Commission. He completed work for his law degree at American University and became an attorney for the CSC in 1960. In 1969, he switched to the Indian Claims Commission and remained there until his retirement.

Mr. Nelson was born in River Falls, Wis., and grew up there and in Redlake, Minn.

He was a member of Masonic Naval Lodge No. 4, a past-master of the King David Lodge of Washington, a member of the Alexandria Consistory of the Scottish Rite, a Noble and Shirner of the Kena Temple of Alexandria, and a member of the Washington chapter of the Sons of Norway. He also was a past-president of the Hawaii State Society of Washington.

Mr. Nelson's survivors include his wife, Myrtle K., of the home in Annandale; a son, Don I., of Mannford, Okla., his mother, Mildred L. Singley and a sister, Joy Leonore Hughes, both of Port Orchard, Wash.