U.S. optimism over Russian economic prospects dimmed following reports that President Boris N. Yeltsin has decided to retain Viktor Geraschenko as head of the nation's central bank.

Control of the Central Bank and the size of the 1993 budget deficit have been key points of contention between the government and parliament. Mr. Yeltsin dissolved Parliament Tuesday and called for elections starting Dec. 11.Jeffrey D. Sachs, a Harvard University economist and Yeltsin adviser, said in a phone interview from Bolivia that he was informed by a Yeltsin cabinet member Wednesday of Mr. Geraschenko's reappointment, adding that the move ''throws cold water" on hopes for economic reform.

Mr. Sachs, architect of Russia's reform program, blamed Mr. Geraschenko for runaway inflation in the Russian ruble and charged him with responsibility for ''destruction of confidence in the currency." Reformers in the Yeltsin government were "quite unhappy" with the reappointment, which promised continued rifts in economic policy, Mr. Sachs said.

Mr. Sachs' comments portraying chaos in Mr. Yeltsin's cabinet and economic policy 10 days before the move against parliament are credited in some quarters with the Russian president's decision to rehire reformer Yegor Gaidar as first deputy prime minister.

Mr. Yeltsin's imposition of economic reforms and his failure to complete them have been alternately blamed for Russia's inflationary morass. Mr. Sachs earlier held out hope that monthly inflation would fall from 20 percent to 5 percent if the Yeltsin government follows through on all of its reform plans.

While some observers have seen Mr. Yeltsin's action as a move to set aside parliament's subsidy-laden budget, Marshall I. Goldman, associate director of Harvard's Russian Research Center, said the crisis was brought on by the ''general disintegration" of the social and economic situation rather than any one factor.

"Yeltsin sait that September would be the month for action," Mr. Goldman said, noting a long course toward confrontation.

In Moscow Thursday, Itar-Tass news agency announced a government resolution signed by Prime Minister Viktor Chernomyrdin gave the Finance Ministry two weeks to draw up outlines for Russia's budget for the fourth quarter and for the whole of 1993, according to a Reuters report.

The government wanted the Central Bank to raise interest rates to defend the ruble and savings banks to raise their deposit rates by at least 30 percent.

Russian interbank rates are about 180 percent, which is well below annual inflation. Consumer prices rose almost 30 percent in August alone, the highest monthly rate this year.

Parliament, stressing the need to protect weaker members of society from the shocks caused by Russia's economic reforms, approved a budget deficit of almost $22 billion or 25 percent of gross national product.

The government said it intended to keep the budget deficit to 10 percent of GNP.

The resolution also told the Central Bank it could only provide funds for parliament with Finance Ministry approval. It also told the Central Bank to transfer almost $200 million of its 1992 profits to the national budget by Oct. 1.