A one-time Law School instructor and right-hand man of former United Nations secretary-general Trygve Lie yesterday leaped 12 stories to his death.

Abraham H. Feller, who graduated from the Law School in 1928 and taught there as an instructor in 1932-33, died immediately after the plunge from his Central Park West apartment.

Feller was reportedly a close friend of Alger Hiss, who graduated from the Law School in 1929. Hiss is now in prison for perjury.

A former New Deal lawyer in Washington, he worked as a liaison agent between the U.N. and Senate committees investigating Communist activities among American personnel of the organization. However, a counsel for the McCarran Senate sub-committee conducting one probe said Feller himself was not under investigation.

Associates said Feller recently had offered his oral resignation from the U.N. post. Mrs. Feller said the recent resignation of secretary-general Lie might have been "a contributing factor" in his death. Feller reportedly wrote some of Lie's most important statements.

Lie said his aide committed suicide because of the "long and serious strain" of defending U.N. employees "against indiscriminate smears and exaggerated charges."

Mrs. Feller attributed his death partly to "fatigue and overwork."