Twice as many Americans surveyed in a Gallup Poll would prefer a new national sales tax rather than a federal income tax increase if the federal government needs to raise more revenue, according to results released yesterday.

The poll of 1,517 adults, conducted April 29 through May 2 for the Advisory Commission on Intergovernmental Relations, also found that 35 percent of the respondents consider federal income taxes the unfairest tax they must pay.

Asked to choose between increased taxes, 52 percent said they would rather pay a new national sales tax on all purchases except food, like the value-added tax in many European countries. Twenty-four percent said they preferred higher income taxes, and 25 percent said they did not know. Respondents also preferred an increase in state sales taxes rather than a higher state income tax by a 57-to-23 percent margin.

But 69 percent of those with a household income of more than $40,000 a year preferred the higher state sales taxes, compared with only half of those earning less than $15,000.

Officials of the advisory commission, which specializes in federalism issues, said many of the respondents may have been reacting to recent increases in Social Security payroll taxes and perceived inequities in the income tax system. Sales taxes are paid frequently and in small amounts, they noted, and consumers can control the size of their payment by restricting purchases.

After federal income taxes, 26 percent of respondents chose local property taxes as the unfairest tax, 13 percent the state sales tax and 11 percent the state income tax. This was a major reversal from 1972, when 45 percent complained most about property taxes and only 19 percent about federal income taxes.

Asked how to make the income tax system fairer, 49 percent said "make upper-income taxpayers pay more." Thirteen percent said "reduce taxes on lower-income taxpayers" and 6 percent said "make business firms pay more." Another 16 percent said "leave the tax system alone--it is about as fair as you ever are going to get."

On a question about reduced federal aid to local governments, 18 percent said their states should try to make up all of the federal cutbacks, 46 percent said only some of the cutbacks and 16 percent said none.