Erosion of labor support for Ronald Reagan in the conservative AFL-CIO building trades indicates trouble may lie ahead for Republicans in fall congressional elections.
Labor's hard-hat unionists frequently have backed GOP candidates in the past. A majority was for Mr. Reagan when he won the presidency in 1980. Undoubtedly, many rank-and-file construction workers still support him, but a conference of the AFL-CIO's Building and Construction Trades Department in Washington reacted coldly to appearances by President Reagan, Secretary of Labor Raymond Donovan, and GOP national chairman Richard Richards.
In marked contrast, representatives of 4.1 million members of building trades unions gave thunderous applause to Sen. Edward M. Kennedy of Massachusetts and former Vice-President Walter F. Mondale, two front-runners for the Democratic presidential nomination in 1984.
President Reagan was booed April 5 when he met with 5,000 conference delegates in an effort to rally support for the administration's program with forecasts of future prosperity.
In introducing Mr. Reagan, Robert Georgine, president of the department, said , ''I don't have to tell you how deep a recession the construction industry has slipped into.'' March unemployment figures showed 1.1 million construction workers, or 17.9 percent, were idle - almost twice the national rate of 9 percent.
High unemployment in the building trades, blamed by unions on tight money policies and high interest rates, sparked most of the loudly expressed dissatisfaction with the President in the coolest reception he has had from any audience since moving into the White House.
A year ago, the department said nothing had appeared to work under Jimmy Carter, so it decided to ''give the new (Reagan) economic program a chance.'' Mr. Georgine told the 1982 meeting that the program ''has had that chance and it doesn't appear that it will work unless it is modified.''
It is up to Congress to do that, he added. If any congressman takes a position, along with the President, that ''unemployment is the price that must be paid to fight inflation,'' said Mr. Georgine, then ''start organizing to defeat him in November.''
GOP chairman Richards drew a chorus of boos when he appealed to construction workers to join ''a national labor advisory committee'' to help develop a ''constructive'' relationship with the Republican Party. He conceded that he was uneasy with the close relations between labor and the Democratic National Committee, fearing an effort ''to move the AFL-CIO into the Democratic Party, officially making the Democrats the party of labor.''
Presidential hopefuls Kennedy and Mondale got ovations for denunciations of Reagan policies, and Sen. Lowell P. Weicker Jr. (R) of Connecticut, a liberal, surprised and delighted the conference with a blistering attack on White House policies. Mr. Weicker called for defeat of legislators who support the President , be they Republicans or Democrats.
Meanwhile, AFL-CIO's Committee on Political Education reports strong support in regional meetings for a campaign to ''turn this country around'' in November. AFL-CIO president Lane Kirkland said local leaders at four conferences held so far believe ''the administration is floundering.'' He predicts the Nov. 2 election will reap Democratic victories.