President Reagan on Tuesday signed landmark trade legislation and told an audience at the bustling West Coast port of Long Beach the new law will keep America riding on a "global wave" of prosperity. He said he was signing the bill despite misgivings over some of its provisions. "We're here to sign a piece of legislation that will help our economy continue to grow and compete," Reagan said during a signing ceremony at the Port of Long Beach, one of the world's 10 busiest computerized cargo ports. The legislation authorizes U.S. participation in current world trade talks, streamlines procedures for retaliatory import curbs against unfair trade practices and makes many other changes in trade laws. "Our administration and Congress have come together in an effort to ensure open markets around the world," Reagan said. "It hasn't been easy, but I have never doubted our ultimate victory, because we're riding a global wave."