The secretary of the Treasury, Henry Paulson, warned that raising taxes on hedge funds and buyout firms may have “unintended consequences” and said Congress shouldn’t “single out” firms that go public, such as Blackstone Group LP.

“I don’t believe it makes sense to single out one industry,” Mr. Paulson said when asked about proposed legislation at a conference hosted by the Wall Street Journal in New York. Senate legislation would force Blackstone to pay taxes at corporate rates of 35% instead of as a partnership, with a burden as low as 15%. “We need to be careful dealing with something like this piecemeal,” Mr. Paulson said.

Mr. Paulson, the former chief executive officer of Goldman Sachs Group Inc., was the second senior Bush administration official yesterday to raise concerns about efforts to increase taxes on many hedge funds and buyout firms. A White House spokesman, Tony Snow, also suggested that the administration will oppose such an effort.

“This is not an administration that’s predisposed toward tax increases,” Mr. Snow told reporters this morning. He said at a later briefing that he was speaking generally and wasn’t addressing specific legislation.

“We’re going to take a look at what Democrats have to offer,” he said.

Shares of Blackstone, which traded as low as $29.13 15 minutes before Mr. Snow’s first remarks, jumped 3.5% to more than $30.40 afterward. Shares of Fortress Financial Group LLC, the first hedge-fund manager to go public in February, increased as much as 6.2% after Mr. Snow’s remarks. Shares of Blackstone fell 83 cents, or 2.7%, to close at $29.92. Fortress shares gained $1.18, or 5.32%, to close at $23.25.

The tax structure of hedge funds and buyout firms has drawn congressional attention in the wake of billion-dollar paydays for fund managers.

The Senate legislation, introduced June 14 by the chairman of the Finance Committee, Max Baucus, a Democrat from Montana, and Charles Grassley, an Iowa Republican, would penalize financial firms that become publicly traded partnerships.

The June 22 House legislation, backed by top Democrats, would tax the share of profits that managers receive for investment services at ordinary income-tax rates as high as 35% and affect all partnerships, public and private. Currently, that income, known as “carried interest,” is taxed at capital gains rates as low as 15%.

Mr. Paulson said other industries use the partnership model, citing real estate and construction. “We have tended to single out companies and industries to respond to the pressures of the moment,” he said. “We need to think comprehensively. We need to be careful of unintended consequences.”