Nearly 500 leaders of the world's largest industrial unions are meeting here this week in an attempt to shore up defenses and plan new strategies for a labor movement that seems to be losing more battles than it is winning nowadays.

That, at least, was the tone of the literature, speeches and interviews marking the opening yesterday of the 25th triennial World Congress of the Geneva-based Interational Metalworkers' Federation, an organization representing 13.7 million autoworkers, aerospace, electrical and shipbuilding employes in 70 communist countries.

This year's meeting will feature three members of Solidarity, the Polish workers union that has become a major political irritant in the family of Warsaw Pact nations and a cause celebe for defenders of free trade unionism. The three workers and an interpreter arrived over the weekend and are scheduled to hold a news conference tomorrow.

The meeting comes at a difficult time for unions: American steel and auto unions are losing thousands of members because of an economic downturn; unions in England are struggling to hold onto disappearing jobs and power in a declining economy, and labor leaders in the U.S. and elsewhere say they have been put on the political defensive.

"Anti-unionism is increasing," said Herman Rebhan, 60, the Metalworkers' general secretary.

"The employers have been encouraged by the political developments to try to take advantage of the situation of economic decline" in developed countries, Rebhan said in an interview. But he added that, despite its problems, the international labor movement is not bankrupt of ideas.

"We hope to discuss some of those at this meeting, to look at those problems and, maybe, to come up with some strategies" to combat the worldwide problem of unemployment, Rebhan said.

He said the metalworkers' conference, conducted under the banner of "Peace, Justice, Jobs," will focus on issues including:

Correcting automation-caused unemployment through the introduction of a shorter work week and shared-work programs in affected nations.

Increasing worker participation on corporate boards of directors and in other management groups.

Developing labor strategies for dealing with multinational corporations, such as auto companies moving into production of the "world car."

Supporting labor movements in South Africa and in Latin American countries, where unions increasingly are being used as surrogate political forces against policies of autocratic governments.

Trying to understand "the real ferment within the labor movement itself," which Rebhan said is undergoing generational changes, with "younger and better educated people coming in," and changes in ethnic composition -- "more blacks in the plants today."