L. Marie Lantz, 72, a retired administrative assistant to Sen. Jennings Randolph (D-W. Va.), died Sunday at the Bay Front Medical Center in St. Petersburg, Fla., following a heart attack. She had been stricken in her winter home in St. Petersburg.

Miss Lantz came to Washington in 1934 and became secretary for Randolph, then a freshman member of the House of Representatives. In those days, House members of Congress were permitted only one personal staff member, so Miss Lantz's duties included administration as well as secretarial work. She remained with Randolph until he was defeated for reelection to the House in 1946.

For the next 12 years, Miss Lantz worked for Rep. Harly O. Staggers (D-W. Va.) and Rep. James Domeneaux (D-La.).

When Randolph was elected to the Senate in 1958, Miss Lantz became his administrative assistant, the top position on Congressional staffs. She remained with the senator until her retirement in 1971. Since then, she had lived in Elkins, W. Va., and St. Petersburg.

Miss Lantz was born in Barbour County, W. Va., and grew up in Elkins. She graduated from Davis and Elkins College in Elkins and worked for a sheriff before she came to Washington.

Survivors include two brothers, Joe Lantz, of Elkins, and Charles W. Lantz, of Lima, Ohio.