Rep. Richard A. Gephardt (D-Mo.) accused two Democratic presidential rivals yesterday of being "content" with President Reagan's "outdated" trade policies and called for immediate enactment of his controversial trade amendment as an assertion of U.S. leadership in international economics.

Gephardt said last month's stock-market crash was "a declaration of interdependence and a call for new American leadership in the global economy." He also charged that Massachusetts Gov. Michael S. Dukakis and Sen. Albert Gore Jr. (Tenn.) are "running for political cover" on the trade issue.

"Unfortunately, there is no cover for the workers who are losing their jobs to unfair foreign trade practices," Gephardt said in a toughly worded speech prepared for a Georgetown University audience and a fund-raising dinner last night.

He jabbed at Dukakis, who has made Massachusetts' economic boom a staple of his campaign, by noting that an auto plant in Framingham, Mass., closed last week with 3,700 workers losing jobs to "the do-nothing approach to foreign trade barriers."

Gephardt's amendment has passed the House and is in conference with a somewhat tougher Senate bill. His amendment would require retaliatory measures such as import quotas or tariffs against nations whose trade barriers bar U.S. goods from their markets.

On Tuesday, the House voted 238 to 175 to defeat a Republican attempt to kill the amendment. Many Democrats also have expressed opposition to it.

Gephardt's rivals criticize it as protectionist, but Gephardt contended last night that it would require negotiations to open closed markets to fair trade. "The Gephardt amendment is really just the Golden Rule, with teeth in it," he said.

"It's not an across-the-board tariff aimed solely at protecting U.S. markets, as we had in the '30s," he said. "It's a reasonable and flexible attempt to remove foreign tariffs."

Gephardt accused his Democratic rivals of sounding like "born-again free traders . . . content with the status quo" and said they actually support "old-style, shortsighted protection for specific industries."

He said Gore's call for presidential action on trade was "empty rhetoric . . . that sounds a lot like Ronald Reagan to me" and that Dukakis' call for limited, short-term protection for vulnerable industries is the approach that "gave us the $170 billion trade deficit we have today."

"If Mike Dukakis or Al Gore or anybody else wants to defend the Reagan trade policy, I'm willing to let them try," he said. "But I am going to continue to stand up for American workers."

Gore's campaign manager, Fred Martin, responded that "Smoot-Hawley-Gephardt is not the answer, either for the country or his stalled campaign."