William French Smith is a private man. For 34 years he has practiced with the same Los Angeles law firm, accumulating great wealth, serving a number of prominent business clients, but leaving few public marks.

Unlike most other attorney generals in recent years, Smith, Ronald Reagan's private lawyer who is now his choice to head the Justice Department, has almost no publicly available record from which he can be gauged.

To some friends and associates, the most surprising thing about his nomination for the Justice job is that he is willing to accept the limelight that comes with the territory.

To Justice Department lawyers and many lawyers in the East, the question is whether Smith's long career as labor lawyer and, more recently, as senior partner of the prominent firm of Gibson, Dunn & Crutcher prepares him for the range of work involving antitrust, civil rights, criminal and civil cases that concerns the Justice Department.

Whatever qualities he brings to the job, he brings the one attribute presidents have reckoned most important in recent years -- he is the president-elect's close friend. Smith, 63, is a member of Reagan's inner circle of advisers and social friends and has long managed Reagan's financial affairs.

When he was asked yesterday how the nation could be sure there would be no special treatment of Reagan by the Justice Department because of the two men's friendship, Smith replied: "The question is the basic integrity of the individuals involved and I think there you will not be disappointed."

Among Smith's few recorded public words are two speeches he made to an annual California political event called the Sacramento Host Breakfast.

In 1965, when the Johnson administration and Congress had launched the Great Society in a time of optimism, Smith warned that federal programs, no matter how well intended, could carry the seeds of America's destruction.

He deplored the concentration of functions at the highest level of government exemplified by the Great Society. "The responsibility of the citizen is being undermined," he said in a speech that raised a possible parallel between the future of the United States and the fate of the Roman Empire. "If it is destroyed, the source of our strength will be dried up. The nation will contain subjects -- perhaps well-fed -- but not citizens."

Like Reagan, Smith, who began to serve as his private lawyer in the 1960s, believes government functions should be done by the smallest unit capable of handling them. Self-governing communities, he said, have their economic counterpart in the free enterprise system.

Smith noted in his 1965 speech that this "is not politically salable as an issue these days."

Nine years later, Smith was invited back to address the breakfast. By then, he had become one of Reagan's closest advisers, political as well as personal. This time, Smith's message to his audience was that businessmen must become more involved in politics.

He spoke of the animosity toward business on campuses and elsewhere in America and urged active attempts to change business' image. "We must also become totally enmeshed in the process of electing public officials who will understand and are sympathetic to the fundamentals of our economic system," Smith said. The public, he added, must be shown the basic coincidence of business interest with the public interest.

California lawyers and others who have watched him work dwell on two of his characteristics -- composure and caution. "I've never seen him lose his cool," said Francis Wheat, one of Smith's partners in his 250-lawyer firm.

"He's got great patience. He's got great stamina," said former California lieutenant governor and secretary of health, education and welfare Robert Finch. "He doesn't try to push a result."

"He doesn't shoot from the hip," added Wheat.

Smith is a very conservative man, but his admirers, Democrats as well as Republicans, think his conservatism is of the brand that respects other views and would stop him from ever running roughshod over anyone.

One civil rights activist raised fears that Smith would abandon all support for affirmative action, but added that no matter who was attorney general he would expect less-vigorous civil rights enforcement from a Republican-led Justice Department.

"Look, I don't agree with Smith on a lot of things, but he knows quality and he's absolutely scrupulous," said a prominent Democrat who has seen Smith in action over many years. "He's not going to be any [John] Mitchell. He just isn't about to do any such thing."

Smith, in a brief telephone interview, was everything his associates say he is: courteous, understated, gently humorous and a man of few words.

He said it would be inappropriate to comment on any aspects of the law at this point.

Smith's specialty has been labor law. However, for the last decade he has not been in the trenches negotiating, but has been advising a number of business clients and spending much of his time on administering his rapidly expanding firm, which recently opened new offices around California as well as in London and Paris.

Smith also has been giving Reagan advice -- advice that appears to have helped increase Reagan's wealth. For years, Reagan's assets have been in a trust managed by Smith, and Reagan is known to follow Smith's advice with full confidence.

Smith recalled that he argued one case before the U.S. Supreme Court. It involved an interpretation of the Fair Labor Standards Act in the late 1950s, Smith said.

Did he win?

"Well, I like to say that 12 federal judges heard the case and they split 6 to 6." He added that unfortunately five of the six against him were on the Supreme Court.

Smith has become a rich man. About nine months ago, he was required to file a partial financial disclosure statement because he is a member of the Board of Regents of the University of California. The regents resisted making such disclosures, but lost in court.

Smith listed holdings worth between $10,000 and $100,000 in each of 21 companies. He owns more than $100,000 worth of stock in two companies -- an oil company called Southland Royalty Co. and General Electric, the corporation Reagan once worked for.

Smith also listed holdings worth less than $10,000 in each of 10 companies.

Like many other wealthy Californians, Smith owns agricultural and other land. He has 281 acres in Riverside County called Rancho California where another Reagan insider, William Wilson, also owns land.

(Smith, Wilson and a third Reagan associate, Justin Dart, are cotrustees of Reagan's 688-acre ranch in Santa Barbara County.)

Smith also owns two parcels, each about 20 acres, in Madera County. The parcels are part of a large agricultural package managed by W. D. Fowler and Sons. Smith has nonagricultural land interests in Santa Ana and near Palmdale, according to the disclosure statement.

Smith is on the board of Pacific Lighting Corp. which owns W. D. Fowler and Sons and, until recently, owned an agribusiness called Blue Goose Growers Inc. Smith is also on the board of Pacific Telephone & Telegraph Co., the California-based subsidiary of American Telephone & Telegraph. The Justice Department antitrust suit against AT&T is scheduled to go to court next month.

Crocker National Bank, Pacific Mutual Life Insurance Co., Jorgensen Steel Corp. (owned by Reagan friend Earle Jorgensen), Pullman Inc. and the Automobile Club of Southern California, are Smith's other corporate directorships. He is also active on the board of several cultural and civil organizations.

Smith was born in Wilton, N.H., and graduated summa cum laude from the University of California in 1939. He graduated from Harvard Law School in 1942 and was in the Naval Reserve from 1942 until 1946 when he joined Gibson, Dunn and Crutcher.

Reagan named Smith to the university board of regents in 1968 as the campus turmoil was beginning to subside.

Several observers remarked that although Smith was received as Reagan's man and tensions ran high, Smith was effective in defusing some of the problems of the time.

One regent at that time said he has no doubt that Smith shared Reagan's attitude toward protesting students: "If you don't like it, get out." Still, this former regent added, Smith was a conciliatory force in public and proved to be a good listener.

Like many good listeners, he uses words sparingly.

"I've seen him negotiate. Some negotiators are machine gun talkers. He says very little," said a former associate, Jan Vetter. "He's not a formidable or intimidating person. He's a human guy, but with him, business comes first," said Vetter, who likes and admires Smith.