In last week's series of bold steps articulating a more aggressive national trade policy -- including a willingness to reverse previous policy and drive down an overvalued dollar -- President Reagan effectively took the steam out of the Democratic Party's backward lurch into protectionism.

With the help of underlying worldwide economic events that may see a modest reduction in the United States' global trade deficit next year, prospects for the grossest kind of protectionist moves -- such as an import surcharge -- probably are dead for this year.

This doesn't mean that America's problem of restoring its competitive edge has been solved, or that there will be no protectionist trade legislation at all, or that the urgent necessity to reduce the awful U.S. budget deficit has been lessened.

But perhaps the most significant development to emerge from recent events is that some influential Democrats have had second thoughts about the long-term political dangers of the party's fast slide into protectionism.

When Congress returned from its late-summer recess, House Ways and Means Committee Chairman Dan Rostenkowski was importuned by the protectionist bloc to put the 25 percent import-surcharge bill (which he had coauthored with Rep. Richard Gephardt of Missouri and Sen. Lloyd Bentsen of Texas) ahead of tax reform legislation. But Rostenkowski wouldn't budge.

"There was a big rush (toward action on trade) in the first two weeks of September," Rep. Donald J. Pease (D- Ohio) told me. "But that (priority for tax legislation) slowed things down. A lot of people had become concerned with the speed with which this (surcharge) bill was moving."

Amazingly enough, the crude surcharge bill, fulfilling the urge to "do something about Japan," had been endorsed by such ordinarily calm heads as MIT economist Lester Thurow, who often provides intellectual resources for Democrats.

Ted Van Dyk, another high-up party adviser, accurately observed in the New York Times that protectionist- minded Democrats had "lost their way," abandoning constructive approaches in keeping with party tradition. And as Michael Barone said in The Post last Sunday, a Democratic policy focused on protectionism and restrained growth, however promising as a short-term jobs issue for 1986, is "not very inspiring stuff for a party that once promised to cure the ills of the one-third of a nation ill-clothed, ill- housed and ill-fed."

So there were good reasons to rethink the drift into protectionism. According to Albert R. Hunt of The Wall Street Journal, top Democratic poll- takers Patrick Caddell and Greg Schneiders warned that the protectionist drive is sure to turn off young voters, whose votes are desperately needed in the next presidential election.

Now, even Gephardt has shifted perceptibly, hinting that a broad-based surcharge may be dropped. In a telephone interview after the president's initiatives were announced, Gephardt told me: "I never said my (25 percent surcharge) bill was perfect, and we're looking at different ways of accomplishing the purpose."

The Democratic initiatives for stronger government involvement in trade and economic issues may now revolve around the more thoughtful ideas of Sens. Bill Bradley, Gary Hart and Max Baucus, and focus on those members in the House Democratic Caucus who argue that Congress' first priority should be to lower the budget deficit, move firmly against unfair trade practices by others and provide a more rational approach to "adjustment assistance" -- money for retraining or relocating workers who lose out to foreign competition.

The protectionist drive within the Democratic Party was blatantly political. Frustrated for the entire first term by a Reagan economic policy that brought the nation to the brink of economic disaster but was not rejected by voters, Gephardt and others believed that in the trade deficit they finally had an issue that exposed the weakness of Reaganomics.

The frustration with unfair trade practices and closed markets is understandable, says Bradley. "But then we tied the trade deficit and the notion of fair market access into a neat little package and shifted the burden . . . onto Japan," he notes.

Soon, the protectionist Democrats began to hear from constituents who realized that tougher quotas on imports, along with punitive surcharges, would bring retaliatory measures. The Farm Belt, which knows that the produce from one out of every three acres goes abroad, was especially concerned.

So, with Ronald Reagan's help, the Democrats may be finding their way back toward open trade policies. According to Rep. Anthony C. Beilenson (D-Calif.), 85 House Democrats are sponsoring a resolution calling for the House Budget Committee to report a new budget plan that will yield a balanced budget by fiscal 1989. That's where the Democratic Party should be going if it wants to put Reagan back on the defensive.