NEW YORK (AP) _ From its Civil War beginnings as a banking-brokerage house on Boston's State Street, Kidder, Peabody & Co. has provided services to more than six generations of business and government leaders, barely surviving the Depression and helping finance America's transformation into an industrial giant.

Henry P. Kidder, Francis H. Peabody and his brother Oliver W. Peabody hung their shingle April 1, 1865, a week before Robert E. Lee and Uysses S. Grant agreed on terms that ended the Civil War.

Kidder, the son of a fish inspector, and the Peabodys, sons of a Unitarian minister, had served more than 15 years as apprentices of J. E. Thayer & Brother, one of Boston's leading private banking and brokerage houses.

When the firm's owner Nathaniel Thayer decided to retire, he gave his business to the three clerks. They opened a Wall Street office in 1868.

By World War I, Kidder Peabody's reputation as an underwriter and distributor of corporate and government securities ranked it among the half- dozen most prominent investment firms in the country. Its clients ranged from the Atchison, Topeka & Santa Fe railroad to the Italian government.

But the company failed to adjust to the aggressive competition spawned in the 1920s, and when the stock market collapsed in October 1929, Kidder Peabody quickly went broke, with nothing left except its still widely respected name.

In desperation, it turned for help to J.P. Morgan & Co., Wall Street's best-known investment bank, which helped organize a cash infusion of $15 million. But Kidder Peabody continued to lose money.

Three new partners took over in 1931. Edwin S. Webster Jr., Albert H. Gordon and Chandler Hovey used the firm's name and reputation, together with their Wall Street connections, to salvage Kidder Peabody at a time when the public image of financiers was at an all-time low.

It was not until the close of World War II that Kidder Peabody regained the respected position it had held at the beginning of the 20th century. It has since emerged as among the top 15 Wall Street investment banking firms in terms of capital, with 6,000 employees in 68 offices in the United States and abroad.

Kidder Peabody has played a leading advisory role in mergers and acquisitions and developed major positions in relatively new markets such as financial futures. The company acted as a manager in more than $100 billion in corporate, municipal and international financings last year.

Its net income has grown at an annual rate of 19 percent in the past five years, and earnings totaled $47 million in its fiscal year ended Nov. 30, 1985.