Milton P. Kroll, 98, an early legal officer at the U.S. Securities and Exchange Commission who helped shape the development of U.S. securities law during four decades in government and private practice, died Sept. 14 at his home in Chevy Chase.

He had respiratory failure, said his son, Stephen Kroll.

Within three years of graduating from Harvard Law School, Mr. Kroll joined the Securities and Exchange Commission in 1940. While working in the Office of General Counsel, he helped develop and put into practice many of the first securities laws, including exploring how far the SEC’s powers reached and different processes for registering securities.

He worked on a successful effort in 1942 to create an extradition treaty with Canada. The SEC wanted the treaty in order to prosecute owners of a Canadian mining venture who were making fraudulent offers in the United States.

Mr. Kroll remained at the SEC during the first years of World War II. He helped the War Department by providing potential enemy bombing targets based on SEC filings concerning overseas factories.

Mr. Kroll served on active duty in the Army in Europe from 1943 to 1945, then returned to the SEC. He rose to associate general counsel before leaving the agency in 1953 to enter private practice.

From 1953 to 1961, he worked with Brown, Lund & Fitzgerald. He then founded Freedman, Levy, Kroll & Simonds, where he remained until 2001. He then served as counsel to Foley & Lardner.

In private practice, Mr. Kroll worked on the development and SEC approval of the syndication of large real estate holdings.

Milton Paul Kroll was a native of Paterson, N.J., and a 1934 graduate of West Virginia University. He was a founding member of Temple Sinai, a Reform synagogue in Washington.

Survivors include his wife of 71 years, Beatrice Rappaport Kroll of Chevy Chase; two children, Stephen Kroll of Washington and Barbara Kroll of Needham, Mass.; and two grandchildren.

— Stefanie Dazio