A photograph taken in the office of the U.S. delegation to the Ottawa economic summit in July 1981 shows Richard G. Darman working at a desk with President Reagan, Treasury Secretary Donald T. Regan, presidential counsel Edwin Meese III and Cabinet secretary Craig L. Fuller standing around the desk apparently concentrating on Darman.

A caption written by the president reads: "Dick -- writing home already? We've only been here about three hours!"

Actually, Darman was drafting talking points for Reagan to use in meetings with French Premier Francois Mitterrand. The episode illustrates how quickly Darman, then 37, became a major factor in the Reagan administration on a wide range of issues after starting out with the relatively modest title of deputy assistant to the president. He became one of the chief architects and tacticians of Reagan's impressive legislative victories in the first years of the first term.

Reagan yesterday nominated Darman, now assistant to the president and deputy to the chief of staff, as deputy secretary of the treasury. There he will continue as No. 2 to James A. Baker III, the White House chief of staff whom Reagan has nominated as secretary of the treasury.

The brilliant, abrasive Darman made his share of enemies over the past four years, some over major disputes, some over petty, personal ones, but he compiled an impressive record.

Darman was the creator and driving force behind the White House's legislative study group, which coordinated the passage of Reagan's tax and budget proposals in the first two years of the administration.

"On such legislation as the Gramm-Latta bills, he understood how to bring pressures to bear, to form coalitions and to anticipate our opponents' arguments," David Gergen, the former White House director of communications, said.

Darman also was instrumental in working out the Social Security compromise, in setting up a bipartisan commission to study the program's financial problems, and then working out the compromises between Reagan and congressional leaders. He is fascinated with solving problems and has a great facility for working out solutions.

"He is completely devoted to public service and building institutions and in leaving the office of the presidency stronger than it was four years ago," Gergen said. "Because of his service in the previous Republican administrations, he brought an institutional memory to the White House. He knew how it and other institutions are supposed to work and their weaknesses and as a result could anticipate a lot of troubles and problems."

Kenneth Duberstein, a friend and chief of White House congressional liaison until about a year ago, said, "He is an outstanding intellect, an articulate political tactician and organizer, a fierce competitor who demands perfection of himself and those around him."

Darman also is a workaholic and perfectionist who inherited those attributes from his father and grandfather, who owned and operated textile mills in Massachusetts. According to one source, one of Darman's regrets to this day is that he scored 790 on one of his scholastic aptitude tests rather than a perfect 800.

"He isn't ambitious for money, or power, or status," one colleague said. "He just has a natural feeling that he's superior to most people and deserves to be at the highest policy level."

According to Laurence I. Barrett, a close observer of the Reagan administration, Darman has "a voracious appetite for increased responsibilities."

He isn't indifferent to power and status, however. He chafed at his original White House rank, deputy assistant to the president, and at descriptions of his job as a "paper shuffler" although he helped draft his job description: "Mr. Darman will be responsible for assuring the full and fair staffing of all papers intended for the president. He will also be responsible for overseeing the management support systems of the White House and for advising the chief of staff on selected substantive issues."

Darman's control of the paper work reaching the president is a great source of power in the White House, but he also bridled at being called "Baker's aide" -- and would correct transgressors that he was assistant to the president. At a recent White House staff planning session for the inaugural, Michael K. Deaver, deputy chief of staff and assistant to the president, announced that Darman would be awarded the first honorary inaugural license plates and presented them to him. They were inscribed: "Baker Aide."

Some colleagues and observers describe Darman as something of a driven man, who is hard to work for and has had considerable staff turnover as a result.

Part of the reason is that he suffers fools badly and is known for bad-mouthing mediocre performances by his colleagues.

He helped engineer the resignation of Anne Burford as director of the Environmental Protection Agency, and was critical of Reagan's first secretary of state, Alexander M. Haig Jr., who suspected him of leaking derogatory information. Meese accused Darman of trying to push him out of the administration two years ago and called him "a troublemaker."

Like Baker, Darman also is distrusted by conservatives, who consider him to be one of an almost defunct political breed, a northeastern liberal Republican. Darman is not particularily interested in ideology and considers himself almost apolitical. His concern is making the government work. Darman believes in effective government, not less government, and he is a protege of Elliot L. Richardson, the personification of the liberal Republican Boston Brahmin.

Darman served under Richardson during the Nixon-Ford administrations as Richardson made his way through the Cabinet -- health, education and welfare, defense and justice -- and wound up as an assistant secretary of commerce, where he met Baker.

Darman grew up in Wellesley Hills, Mass., the son of an indutrialist. Darman was captain of the football, lacrosse and wrestling teams in prep school and played lacrosse at Harvard, where he met Kath, a Radcliffe student, who became his wife.

After graduating from Harvard Business School, Darman joined the then-Department of Health, Education and Welfare, where he caught Richardson's attention. With Richardson, Darman resigned from the Justice Department in Watergate "Saturday Night Massacre" in October, 1973.

He did not work in Reagan's 1980 campaign except to help rehearse Reagan for his winning debate with President Carter. Four years later, Darman was to take much of the blame for Reagan's comparatively poor showing in his first debate with Democratic presidential nominee Walter F. Mondale (Reagan was "brutalized" by facts and statistics, Sen. Paul Laxalt charged). After the Nov. 6 election, Darman took credit for many of the major decisions that led to Reagan's landslide.

This is a matter of dispute, but the range and quality of his work in the White House over the past four years is not.

As one person put it: "He started with advantages and he's made the most of them."