His real name was Manuel Frederick Cohen, but no one ever called him anything but Manny."

The feisty lawyer from Brooklyn, the first man to rise through the ranks to become chairman of the Securities and Exchange Commission, died Thursday after a heart attack in his law office in Washington. He was 64.

Mr. Cohen, flamboyant and tough, and a man of enormous energy, had a bigger impact on Wall Street and the brokers who run the stock markets than anyone in his job before or since. Prodded and harassed by Mr. Cohen, the exchanges and the mutual fund industry were forced into changes designed to protect and make more secure the position of the average shareholder.

Mr. Cohen joined the SEC staff in 1942 as a junior attorney and stayed 27 years. He rose through the bureaucracy and was director of the division of corporate finance when President Kennedy named him a commissioner in 1961.

In 1964, President Johnson promoted him to the SEC chairmanship. It was at a time when morale at the SEC was at a relatively low ebb. A special independent study of the securities markets in 1963 and pointed to the need for reform and regulation, and the seemingly successful mood in Wall Street was to resist any disturbance of the status quo.

But for five years, or until President Nixon unceremoniously dumped him in 1969, Mr. Cohen was a prickly thorn in the side of the securities industry. He rocked "the Street" with efforts to get rid of "insider trading" abuses and the questionable practice of shared commissions, to reduce mutual fund management fees and to investigate the growing impact of institutional investors on the stock markets.

Increasingly he became concerned about and spoke out on a trend toward the concentration of economic power, especially the formation of conglomerates, which he charged, made less rather than more information available for judgments by investors.

Mr. Cohen publicly took on the American corporation as an institution "invested with political powers," suggesting in a widely discussed speech to the Detroit Economic Club in February, 1969, that there should be some checks and balances on corporate power.

Shortly after the Detroit speech and just before he was to testify before the House Commerce Committee on various securities industry problems, Nixon fired Mr. Cohen and named as his successor Republican Hamer H. Budge.

During the presidential campaign in 1968, Nixon had sent a letter to 3,000 securities industry executives, charging the Johnson administration with heavy-handed bureaucratic regulatory schemes."

Nixon did not mention the SEC by name, but the intended reference was clear. Mr. Cohen responded. "We should not be ashamed to regulate. Regulation is not a dirty word."

Wall Street found Manny Cohen abrasive and too voluble. He once said about himself, "I make a speech when I answer a question." But the movers and shakers in the Street came to respect his knowledge of the industry and his integrity. Former New York Stock Exchange President Robert Haack, as Mr. Cohen was ousted from the SEC chairmanship, said he had been "outstanding" and that the industry had benefited from many of the changes demanded by Mr. Cohen.

Mr. Cohen could have stayed on the commission as a member until 1971, but he returned to private law practice as a partner in the firm of Wilmer, Cutler & Pickering here, where he was much in demand as counsel to investment companies and by others with business at the SEC.

Lately, he sported axe-handled side-burns, and clearly enjoyed a new phase of life with relative financial affluence in marked contrast to his humble beginnings in Brooklyn. Mr. Cohen's father had been a driver for Borden's milk company, and the younger Cohen often helped his father hitch up the horse and buggy to make deliveries or did the driving.Later, the elder Cohen became a candy store owner.

In the last few years, Mr. Cohen also had advised clients concerned with securities industry matters in Israel, the Republic of China, Canada, Brazil and several European countries.

Mr. Cohen was born in Brooklyn in 1912, received a bachelor's degree from Brooklyn College and a law degree from Brooklyn Law School. He was in private practice in New York from 1937 to 1942 before joining the SEC staff.

A resident of Bethesda, he is survived by his wife, Pauline Grossman Cohen, a daughter, Susan D. Borman, a judge in the Recorders Court of Detroit, and a son, Jonathan W. of San Francisco.