The dramatic shift of White House chief of staff James A. Baker III to the post of Treasury secretary -- the nation's chief financial officer -- is yet another signal from President Reagan that his second term will focus on traditional and conservative Republican objectives, distant from the right-wing extreme of his party, observers said yesterday.

Baker's projected switch with Treasury Secretary Donald T. Regan, who will become Reagan's chief of staff, left the business and financial community uneasy, for the most part, because Baker's specific views on broad domestic and international issues are not well known.

But Wall Street analyst Sam Nakagama, typical of some financial experts who have soured on Regan, said in a telephone interview: "I can't think of a better thing that could have happened."

Although Baker has not had wide experience in business, Nakagama pointed out that Baker, a lawyer, has been a director of the highly regarded Texas Commerce Bank of Houston, and also has served in the Department of Commerce.

Baker, moreover, has been one of the chief architects, along with Sen. Robert J. Dole (R-Kan.), of three tax-boosting bills designed to shave back the huge federal deficit.

"I think it's great," Nakagama continued. "Now, we'll have the two leading moderate conservatives, Dole and Baker, running the country."

Some business and financial leaders were critical of Regan for insisting that budget deficits are unrelated to high interest rates, for jawboning bankers to lower their charges to customers and for his persistent complaints about Federal Reserve policy.

Clearly, the economic power structure of the Reagan administration is in the process of being completely reshaped. The troika of economic policy makers of the first Reagan term included Regan, Office of Management and Budget Director David A. Stockman, and Chairman of the Council of Economic Advisers Murray L. Weidenbaum, who was replaced in 1982 by Martin S. Feldstein. On rare occasions, the group was joined by Fed Chairman Paul A. Volcker.

But the troika dwindled to two last summer with the resignation of CEA Chairman Feldstein, who broke with the administration on tax and budget policies. Reagan, who appears to be in no hurry to name a new chairman, may leave the post vacant or downgrade its functions.

Stockman's influence has never been the same since his own critical assessment of Reagan's economic policies became public in an Atlantic Monthly article in late 1981. He is expected to resign some time after the presentation of the fiscal 1986 budget. If he does, and isn't replaced with a strong figure, the troika would then have dwindled to one -- Baker, as the new secretary of Treasury.

Inevitably, many observers said yesterday, that will enhance the role and importance of Volcker and the Federal Reserve. Some even speculated that Volcker -- thought to be planning to resign within the next 18 months or so -- might choose to stay longer if he sees reason to worry about the conduct of fiscal policy.

Another way of looking at the reshaping of the economic policy-making apparatus, suggested former Lyndon Johnson aide Horace Busby, is that the Reagan troika plus Volcker is being superseded by another group of four in which powers are shared between the executive and Congress.

Busby, who sees Regan as a confidante of the president sharing an important role in the centrist reorientation of the Republican Party, said the real foursome now lines up this way: Baker, Dole, Regan and Sen. Robert Packwood (R-Ore.), chairman of the Senate Finance Committee.

Other political experts interviewed yesterday agreed with Busby that a new alliance between Baker and Dole was probably the most likely and significant outcome of the Baker-Regan job trade. But some thought that the new economic power bloc could be better defined as a troika that included Baker, Dole and Volcker, with Regan effectively divorced from economic policy making.

Stuart Eizenstat, who was an aide to former president Jimmy Carter, praised Reagan's choice of Baker for the Treasury post, saying, "he's very smart, with a good head for business and finance."

In a phone conversation from Washington University in St. Louis, Weidenbaum said that Baker would be quite comfortable with domestic economic affairs after four years of close work with Regan on at least three tax bills and the Treasury tax simplification plan.

Eizenstat and Weidenbaum agreed with others when they said that Baker's most difficult job would be learning the intricacies of international debt and finance.

Among the many unanswered questions yesterday is whether Baker will keep Regan's top staffers at Treasury, including Deputy Secretary Tim McNamar and Undersecretary for Monetary Affairs Beryl Sprinkel. Sprinkel, who on occasion has drawn fire from foreign governments for his adamant stand against intervention in foreign exchange markets, campaigned actively for the Reagan-Bush ticket.

That led to rumors that he was under consideration for appointment as CEA chairman to succeed Feldstein, who in his two years in the post was engaged in an almost continuous controversy with Regan.

Also unclear is the fate of the revolutionary tax reform proposals nurtured in the Regan Treasury. It will be up to Baker, as secretary, to carry the fight for tax reform on Capitol Hill. But the administration had already indicated on Monday -- prior to announcement of the Regan-Baker job switch -- that it would negotiate with Congress on tax reform, rather than endorsing the Regan plan.

Eizenstat suggested yesterday that the combination of the president's decision to withhold his blessing from the Regan tax plan, coupled with the delays occasioned by the confirmation process for Baker, might slow down any momentum that may have existed for tax reform.