Thomas Gardiner (Tommy) Corcoran, 80, a leading architect and lobbyist for much of the legislation establishing President Franklin D. Roosevelt's New Deal, and one of this city's most prominent lawyers since the early 1940s, died of a pulmonary embolism yesterday in the Washington Hospital Center.

Mr. Corcoran and his colleague in government, Benjamin V. Cohen, were a team who came close to revolutionizing American government in the early New Deal days. In the process, Mr. Corcoran became an almost mythical hero to Rooseveltians, who viewed the New Deal as a bright light at the end of the tunnel of depression. By the same token, he became a symbol of irresponsibly destructive experimentation to Roosevelt's equally dedicated opponents.

He was not underrated in either camp. His legal scholarship, vitality and wit made him a formidable innovator and advocate. In the early 1930s, "Corcoran and Cohen" entered the language of political controversy as though the two names were a single word: "Corcorancone." It was a word much used in congressional and campaign debate. In Wall Street and business board rooms it was a pejorative.

Yet when he left the government in 1940, Mr. Corcoran's law office was besieged by some of the same corporate leaders who most volubly had denounced him when he was a government official. So many became his clients that his law firm, Corcoran, Foley, Youngman, and Rowe, grew and prospered through subsequent decades. Newspapers usually identifed him in his private career as a lawyer-lobbyist. He called himself a lawyer-entrepeneur.

Mr. Corcoran and Cohen were among the first of the bright young Harvard Law School alumni recommended for service in the New Deal brain trust by Felix Frankfurter, then a professor on the school's faculty.

Both Mr. Corcoran and Cohen had practiced law in Wall Street and were knowledgeable about the operations of securities exchanges, so their first assignment was to draft the Securities Act of 1933. Under orders from the White House, but working with legislative leaders --especially House Speaker Sam Rayburn -- they pushed the reform legislation through in record time.

Their collaboration later accounted for the Securities and Exchange Commission Act of 1935 and the Public Utilities Holding Company Act of 1935. They also contributed to the Federal Housing Administration Act of 1934.

Their reputations made by these successes, they went on to legislation establishing the Tennessee Valley Authority and Fair Labor Standards. They also took a hand in enactment of the Wage and Hour Law. These were among the most important and enduring of New Deal reforms.

The National Recovery Act, another key measure, which the Supreme Court ultimately invalidated, was not a Corcoran-Cohen product. Neither was the so-called court-packing plan, which Congress rejected, although Mr. Corcoran supported it as an administration lobbyist.

Through all the years they worked together as a Roosevelt task force, contriving legislation that would stand up in the predominantly conservative courts and engineering it through congressional committees dominated by orthodox politicians, Mr. Corcoran and Cohen held relatively obscure positions in the executive bureaucracy. Neither ever was officially on the White House staff. Their salaries through most of their government careers were $8,000 a year.

Both bachelors, they lived with a group of congenial young lawyers in what was called "the little red house in R Street," the former summer residence of President U.S. Grant. In those times Mr. Corcoran and his friend were said to have a "passion for anonymity." Both felt that their jobs could best be done out of the spotlight. By cooperating with certain reporters, they managed for a time to keep their names out of print or, at most, on the inside pages.

Whatever anonymity Mr. Corcoran and Cohen had achieved ended with the fight over the so-called "death sentence," imposed by the Utility Holding Company legislation.

Sen. Owen Brewster of Maine, who had been one of the supporters of the legislation, changed sides in mid-conflict. When Mr. Corcoran remonstrated with him, Brewster reported that he had been threatened with cancellation of plans for a hydroelectric plant in Maine.

At a congressional hearing, Mr. Corcoran denied threatening Brewster. Brewster called him a liar.

"We'll see who's a liar," Mr. Corcoran replied.

From then on, Mr. Corcoran's cover, such as it was, was blown. That committee, like many others over the years, failed to censure or even reprove Mr. Corcoran, who had a winning way with House and Senate committees.

All pretense that the team of Corcoran and Cohen operated without White House credentials was abandoned after the Brewster uproar.

Mr. Corcoran did not have direct access to Roosevelt until 1935. Joseph P. Kennedy happened to remark to Roosevelt that Mr. Corcoran could sing admirable Irish ballads and sea chanties, and Mr. Corcoran was called to the White House, where he subsequently became a frequent guest and presidential counselor. Roosevelt called him "Tommy the Cork."

Mr. Corcoran became an invaluable administration operator, with a network of friends forged in the executive branch, federal agencies, and in Congress. He influenced judicial appointments and worked on the president's political speeches. He had a gift for the language that put lilt into oratory.

He traveled with the president on campaign trips and became involved in the unsuccessful attempt to "purge" certain anti-New Deal Democrats in the 1938 elections. Ten years later, Mr. Corcoran suffered another failure: the attempt to nominate William O. Douglas for president in place of Harry S Truman.

Mr. Corcoran was born in Pawtucket, R.I. His father, Patrick, was the son of an Irish immigrant and a leading lawyer and Democratic politician. His mother's family had moved south from Nova Scotia.

At Brown University, Mr. Corcoran worked as a dance band pianist, won academic prizes, and was graduated at the head of his class. He moved on to Harvard Law School, where he again led his class, then became a law secretary to Justice Oliver Wendell Holmes Jr. After an interlude at the court, Mr. Corcoran went to Wall Street, where he practiced from 1926 to 1932.

Mr. Corcoran came to Washington in 1932 to work for the Reconstruction Finance Corp. under Eugene Meyer. With the advent of the New Deal, the RFC became a model for several other government agencies and its personnel was scattered through them. Mr. Corcoran was transfered to the Treasury Department where he worked for Dean Acheson, then its under secretary. He later returned to the RFC, where he stayed for the remainder of his government career.

He began the private practice of law in Washington in 1941, saying that his personal fortunes needed mending and he wanted to get out from under the Hatch Act, which outlawed political activity by government employes.

A few months after retiring from government service, he told a congressional committee that he was earning about $100,000 a year. That was just the beginning. He plunged into corporate law on a grand scale, representing major businesses before federal departments and agencies.

One of his first and most important clients was Sterling Products, a pharmaceutical company whose export affiliate was headed by his brother, David. Sterling and its subsidiaries had contracts with the German giant, I.G. Farben industries, which limited Sterling's operations in Latin America. A consent decree in response to an antitrust suit had the effect of opening Latin America to Sterling. Mr. Corcoran was instrumenatal in bringing about this result.

Another of Mr. Corcoran's clients was the Tennessee Gas Transmission Co., which grew into an enormous conglomerate. At one point Mr. Corcoran was accused of impropriety in conferring privately with members of the Federal Power Commission for his client.

He represented many defense contractors in wartime, and several times was called upon to defend his methods before committees of Congress. He staunchly defended his legal methods. Other clients included Burlington Industries, the United Fruit Co., and American International Underwriters.

One of Mr. Corcoran's preoccupations through the war and beyond was Gen. Claire Chennault's Flying Tigers, American volunteer fighter pilots who flew missions against the Japanese before Pearl Harbor.

Sterling gave Mr. Corcoran's brother, David, a part-time leave of absence to manage an organization called China Defense Supplies, to support the Flying Tigers with American material. Thomas Corcoran served as lawyer for the organization, and soon was wrestling with the problem of shipping supplies around the world through Brazil, Africa, India and across the Himalayas -- "over the hump" -- to the Far East.

After the war, Mr. Corcoran retained his interest in the two civilian airlines spun off from the Flying Tigers. One of them, C.A.T., was sold to the Central Intelligence Agency for operations in Indochina. The other, retaining the Flying Tiger name, continued.

Because of their work together, Mr. Corcoran became a close friend of Chennault and the general's China-born wife, Anna.

Mr. Corcoran's involvement in Washington politics survived the war and Republican administrations. Sen. William Proxmire (D-Wis.) once accused him of lobbying for the confirmation of James R. Durfee's appointment to the Court of Appeals, a nomination that Proxmire opposed.

On another occasion Mr. Corcoran interceded with the then-House Speaker Carl Albert (D-Okla.) against some consumer legislation. In this matter, Mr. Corcoran spoke for U.S. Chief Justice Warren Burger, who feared that the legislation would clog the court system.

One of Mr. Corcoran's newer enthusiasms was the Waterville Valley Ski resort in New Hampshire, a development he had dreamed of since his youth. The project is headed by Thomas Corcoran, David's son, who once was an Olympic skier.

Mr. Corcoran's wife, the former Peggy Dowd, died in 1957. His survivors include four sons, Thomas Jr., of Washington, Dr. David, of Bethesda, Howard, of Potomac, and Christopher, of Newfoundland, Canada; a daughter, Cecily Kihn of Philadelphia; two brothers, David M., of Waterville Valley, N.H., and Judge Howard Corcoran of Washington.