President Carter installed his new economic team yesterday in a somber White House ceremony, marked by fresh pledges to continue existing tax and budget policies in the face of what Carter called "troubled times."

G. William Miller, sworn in at the East Room ceremony as secretary of the Treasury, and Paul A. Volcker, who took the oath as Miller's successor as chairman of the Federal Reserve Board, were, if anything, bleaker than the president in their depiction of economic conditions.

Miller said the administration faces "a towering challenge" in coping with the "virulent cancer" of double-digit inflation, "deeply embedded in our economic structure."

Volcker, moving up from head of the Federal Reserve Bank of New York, said the administration is "face to face with economic difficulties unique in our experience. We've lost the euphoria we had 15 years ago that we had all the answers..."

Despite this somber diagnosis, Carter said he was "determined to maintain a steady course." Neither he nor his two appointees made any reference to official forecasts that the recession now under way may push unemployment beyond the 8 percent level. Nor did they acknowledge rising pressure in Congress for passage of a tax cut.

"Now is no time to change course or deviate," Carter said.

An unusually large crowd of guests - many of them from the financial and business community and the economic committees of Congress - turned out to see Judge A. Leon Higgenbotham Jr. of Philadelphia, a member of the 3rd U.S. Circuit Court of Appeals, administer the oaths to Miller and Volcker.

Carter praised both appointees as "superbly qualified men," who, he said, enjoyed the confidence of leaders both here and abroad. He said Miller, like his ousted predecessor, W. Michael Blumenthal, would serve as "chief economic spokesman and economic coordinator" for the administration.

Earlier in the day, Carter received a visit from 16 supportive leaders of the African Methodist Episcopal Zion Church, who praised his policies on human rights and his opposition to recognition of the new government in Zimbabwe-Rhodesia.

Bishop Alfred G. Dunston Jr. said they "did not talk politics" with the president, but said they support Carter on a "spiritual and moral level" because of his "sensitivity to the needs of all people."

Today, Carter takes his campaign for energy legislation on the road again, visiting a neighborhood conservation project in Baltimore and addressing a Sons of Italy luncheon there.