IT WON'T BE LONG - maybe just a century or so - before the wood-paneled, conservative splendor of today's law office is obsolete. Lawyers, as one vision goes, will dole out advice in the basement of Sears, next to the Allstate insurance man.

Picturephones will take the place of human contact in the law office. Thick, cumbersome casebooks will be summarized in information banks and data will be retrieved at the touch of a button. Judges will be replaced by computers that will digest facts and spout forth decisions.

Such notions about the promise of high technology in the next century are the work of a small group of thinkers called "futurists" who study, forecast and conjure up designs and shapes for society in the future.

They don't like the idea of crystal balls. They prefer to anticipate what's to come. And when they think about law they foresee other changes that will shift the course of law.

"The high priest mystique" that surrounds lawyers and the conservatism of a profession that "has at least one foot in the past" combine for resistance to change, said New York lawyer Harold L. Strudler, who gave up an estates practice years ago to study the future.

But, "people who wrap themselves up in a mystique are not entitled to do so if they can't perform," Strudler said. Public scrutiny comes - as it has already to the legal profession - and then change.

University of Hawaii political scientist James A. Dator, a futurist with a special interest in law and government, foresees a rising level of dissatisfaction with lawyers, disgust with manipulation by lawyers and futurists to the point where people will look for ways to make decisions without lawyers - like neighborhood councils.

In an "entirely fanciful" exercise, Chicago lawyer Peter L. Rossiter, once a clerk to Chief Justice Warren Burger, took some numbers about the proliferation of lawyers and law over the past 30 years and made some predictions about the future.

Simple arithmetic said the law and the lawyers would be running amok.

In 100 years, there would be seven million lawyers, one for every 43 of us, Rossiter wrote in an article published in the American Bar Association Journal. Litigation "will have become the single most popular form of human endeavor," the size of some law firms would balloon to 5,000 members.

Of all those millions of lawyers, 60,000 would be judges and 3,500 would preside over the federal courts, according to Rossiter's computations. At the U.S. Supreme Court, there would be 200,000 requests for review and each justice would need a minimum of 12 law clerks compared to the three to four they have now.

Rossiter would be the first to agree that such predictions are unrealistic. Lawyers and cases don't neatly multiply over decades. In a complex society, such straight extrapolation is absurd. Change in the legal profession will reach far beyond the numbers.

At least that's what the futurists say.

In some far away decade, the "lawyer" species may become rare "There will probably be fewer lawyers as we know them," said Harold Strudler, "although there will be a lot more people involved in the law."

Edgar Cahn, co-dean of the Antioch School of Law here, said that "most of the discussion of the future of law assumes that just as you have crisis health care you'll have crisis legal care . . ." Delivery of those services, through legal clinics for example, will produce new kinds of manpower, the legal equivalent of x-ray technicians, nurses, and orderlies, Cahn said.

The Bureau of National Affairs, in a recent publication called "FutureLaw: Lawyers Confront the 21st Century," says the future lies in low cost, prepaid legal plans - legal insurance for the middle class. BNA foresees advertising and marketing flourishing to the extent that a person will eventually find his lawyer in Sears.

The Securities and Exchange Commission last week heard Charles Halpern, director of the Institute for Public Representation, defend the institute's proposal that the SEC adopt a rule defining an attorney's responsibility when he knows a client has defrauded the SEC.

The proposal calls for the attorney to blow the whistle to the commission if a client refuses to do so. It also asks the commission to adopt for disclosure within the corporation when lawyers discover evidence of illegal activities. Halpern told the five commissioners at a packed meeting Tuesday that such rules would help define the lawyer's responsibility and would assist in effective enforcement of securities laws.

The commissioners were not enthusiastic.

"There is a feeling that if we went forward we would precipitate a confrontation with the securities bar, and that is not something we need at the moment," Commissioner Philip Loomis Jr. told Halpern.

Halpern encouraged the commissioners to at least publish the proposed rule and generate comment within the bar.

According to the Legal Times of Washington's annual survey of firms here, nobody comes close to bouncing Covington and Burling out of the Number 1 slot in terms of size, with 200 lawyers and 23 expected hires.

Arnold and Porter, with 132 lawyers moved into second place over last year's Arent, Fox, Kintner, Plotkin and Kahn, which dropped to fifth. Third and fourth this year are Hogan and Hartson and Wilmer, Cutler and Pickering. Jones, Day, Reavis and Pogue dropped from ninth to 25th place, following a split with a group of attorneys early this month. That produced a new firm - Crowell and Moring - which ranked 17th.

The survey says 161 out-of-town firms now have space here. The biggest firm - with 78 lawyers - is Morgan, Lewis and Bockius, and the fastest growing is Akin, Gump, Hauer and Feld, the firm where Robert Strauss was a partner before he became the U.S. special trade representative.

Atlanta's King and Spalding - a firm with which Attorney General Griffin Bell once practiced - opens an office here this week, Legal Times says.

OBITER: Dan J. Bradley, 39, a native of Warm Springs, Ga., and a long-time poverty lawyer and administrator, has been named president of Legal Services Corporation, which provides free legal assistance to poor people in connection with civil cases . . .Assistant U.S. Attorneys E. Lawrence Barcella, deputy chief of the major crimes division here, and Eugene M. Propper, chief prosecutor in the Orlando Letelier case, each received $1,100 special achievement awards from the Justice Department last week for their investigation into the 1976 car-bombing murder of Letelier, a former Chilean ambassador, and an aide . . .The Judicial Conference for the District of Columbia Courts will begin at 1 p.m. Thursday at the Sheraton Park Hotel. Sessions will be held all day Friday.