With more than a million building tradesmen unemployed in the United States - a rate slightly over 25 percent nationally - President Reagan and the Republican Party face the loss of political support from powerful building trade unions, their closest friends in organized labor.
Robert A. Georgine, president of AFL-CIO's Building and Construction Trades Department, warned the White House that the country is in ''one of the worst economic slumps in the nation's history'' because the administration has hung on too long to ''the 'trickle down' economic policy that simply cannot work in an economy as complex as ours.''
Mr. Georgine, who has maintained friendly ties to the administration, sharply criticized ''right-wing theorists and idealogues'' in the White House and Congress, and promised intensified political action to elect lawmakers who will take immediate action to turn the economy around.
''If our elected representatives are not willing to take positive steps to support American workers and the American economy, then we must elect others who will,'' he says.
The building trades leader, one of the most powerful trade unionists in the country, told a convention of the Sheet Metal Workers in New York and a pension investment conference in Kiamesha Lake, N.Y., last week that construction workers nationally ''simply cannot afford to sit on the sidelines, inactive. . . . More than ever before, we must work to organize workers in every district and every precinct.''
Construction unions representing more than 3.8 million workers are angry about the ''deeply depressed'' construction industry blamed on high interest rates, tight money policies and, they say, ''the bulging federal budget deficit'' brought on by last year's ''untested theory of supply-side economics.''
Some 90 percent of bricklayers are unemployed in north-central Ohio and 85 percent of plasterers in Harrisburg, Pa., are jobless. According to AFL-CIO, rates run higher than 50 percent in many crafts in widely separated parts of the country.
Along with intensified political action, the building trades unions are pressing for larger investments of labor pension money in job-creating construction work. The Building and Construction Trades Department's goal is to persuade unions to channel $500 million to $1 billion of the ''multibillions'' in pension funds into socially important projects.