President Reagan said Saturday that he is looking forward to the economic summit in Toronto and warned Congress not to "try through protectionist measures to seal America off from trade and investment with the other countries of the world."

In his weekly radio speech, delivered from the presidential hideaway at Camp David, Reagan reiterated his pledge to work with Congress to reshape the trade bill that he vetoed.The Senate sustained the president's veto on Wednesday.

"Make no mistake, the global economy is the basis of our prosperity and the foundation of our economic future," the president said. "I can think of no surer way of derailing our economy than to try through protectionist measures to seal America off from trade and investment with the other countries of the world."

But Rep. Richard Gephardt, D-Mo., said in the Democrats' response that the trade bill was needed "to put our economic ship of state back on course."

"We can't continue to follow the course set by this administration," Gephardt said. "We've seen our position as the world's largest creditor nation erode to that of the largest debtor. We continue to run historic trade deficits.

"The plain and painful fact is that without any incentive for reciprocity, many of our trading partners are using our outdated assumptions to take advantage of us," Gephardt said.

"This will be my eighth and final economic summit, and there will be much to celebrate," he said.

"Perhaps foremost will be the worldwide economic revolution that has unleashed ever greater levels of prosperity with lower tax rates," he said.

He said that America had led the way in tax cuts and market-oriented economic policies and that the other industrialized democracies had followed.

"It's not surprising that country after country has followed us on the path to greater economic freedom and began to replace their statist policies with deregulation, privatization and freer trade," the president said.

Reagan described the trade agreement reached by the United States and Canada last year as "one of the historic events of our time." The agreement is designed to eliminate trade barriers between the two countries by the end of the century.

"This agreement, looked at in the sweep of history, is truly a gift to the world," he said. "It creates a model that can be imitated and expanded and ultimately made universal among free nations, and that's something we can truly be proud of."

Turning to his dealings with Congress, Reagan said, "I want to reaffirm my commitment to enactment this year of responsible trade legislation."