The unions also said they would soon announce the creation of a rival building trades group, the National Construction Alliance, that would include the carpenters, the bricklayers, the iron workers and the Teamsters. The new group, officials from the two unions said, would have more than 1.5 million members and would be more vigorous than the Building and Construction Trades Department in unionizing construction workers.
"We cannot stand idly by, tied to a past that promises only further decline for construction workers," said Terence M. O'Sullivan, president of the Laborers International Union of North America, which has 700,000 members. He indicated that his union would soon quit the A.F.L.-C.I.O., following five other unions that have left the federation in the past year.
Mr. O'Sullivan and Vincent J. Giblin, president of the International Union of Operating Engineers, said the Building and Construction Trades Department had been ineffective in stopping a decline in construction union membership. The percentage of construction workers who are unionized has plunged to 13 percent today from 40 percent in 1973.
In recent days, officials with the A.F.L.-C.I.O. and several construction unions have engaged in intense talks with Mr. O'Sullivan and Mr. Giblin to try to persuade them not to quit the building trades department.
"We're saddened by their decision to leave," said Sean McGarvey, the department's secretary-treasurer. "This is a net negative for unionized construction workers as we're faced with one of the biggest building booms ever."
He said some builders might grow more reluctant to deal with unions if they risked being called on to sign differing contracts with rival construction federations.
The laborers and operating engineers, which has 400,000 members, had threatened to quit the building trades department unless four demands were met: replacing the department's leaders; trimming its budget; having a voting system of one worker, one vote; and updating a system several decades old for determining which unions are to have jurisdiction over which types of work.
Mr. McGarvey and A.F.L.-C.I.O. officials said they had gone far to satisfy Mr. O'Sullivan and Mr. Giblin on all but one demand: replacing the leaders of the building trades department.
Mr. Giblin said yesterday that the department's current leadership was indecisive, ineffectual and directionless. But several union presidents rejected the demand for new leadership and rallied behind Edward C. Sullivan, the department's president.