Without naming BlackRock, federal auditors have warned that any private parties that purchase distressed assets on the government’s behalf could use generous federal subsidies to overpay, artificially pushing up the price of similar assets that they manage for their own portfolios.

“In other words, the conflict results in an enormous profit for the fund manager at the expense of the taxpayer,” Neil M. Barofsky, the special inspector general for the Troubled Asset Relief Program, wrote in a report last month.

Some of BlackRock’s advice to the government has in fact helped the company. For example, in its role as an informal adviser, it urged the Fed to intervene in the markets in a way that made investors feel it was safe to put money back into money market funds, including BlackRock’s.

The Federal Reserve will not reveal what it is paying BlackRock, disclosing only that on one of its five contracts, it will pay at least $71 million over three years to BlackRock and other firms to manage a portfolio of mortgage assets once owned by Bear Stearns. BlackRock says that rate is discounted and that the fees it collects on bailout-related work are only a tiny portion of its overall revenue.

BlackRock has many admirers for the range and the quality of services it has provided to the federal government. James R. Wilkinson, who served until January as the chief of staff to the former Treasury secretary, Henry M. Paulson Jr., described BlackRock’s co-founder and chief executive, Laurence D. Fink, as a “patriot.”

He added, “He is willing to help our country when we need it most.”

Mr. Fink said he was proud that his company was helping pull the economy back from the brink, and he bristled at the suggestion of impropriety.

Treasury and Fed officials have begun to take precautions. BlackRock’s dominance has prompted the Fed to seek an alternative partner as it prepares to expand its rescue efforts, a government official close to the situation said, requesting anonymity because the actions could affect the market.