A coalition of 10 national labor union presidents and numerous liberal Democratic groups, concerned about what it perceives to be the rightward drift of the Democratic Party, opened a three-day conference last night at the Washington Convention Center to chart "New Directions" for the Democrats.

With the slogan "One Republican Party is more than enough," more than 1,000 Democratic activists representing most of the party's left wing are gathering to attempt to revitalize "the heart, soul and muscle of the Democratic Party," according to conference convener Michael Harrington, chairman of Democratic Socialists of America.

Harrington and Ann F. Lewis, director of Americans for Democratic Action, said they organized the meeting because they think that many Democratic Party leaders are abandoning the party's traditionally strong commitment to "progressive" tax and economic policies and social programs in the mistaken belief that voters have moved sharply toward right-wing values.

"The American people think that Ronald Reagan is a marvelous, wonderful president, but they disagree with him on everything else. The American people have not turned to the right" and would support Democrats if their programs stressed "economic democracy," Harrington said at a news conference at the National Press Club.

The meeting of groups representing labor, minorities, women, senior citizens and others is the first major national gathering of the party's left wing since the 1984 election. It coincides with a weekend meeting in Atlanta of the Democratic Policy Commission, representing the effort led by Democratic National Committee Chairman Paul G. Kirk Jr. to plot the party's future course.

DNC spokesman Terry Michael said Kirk has no involvement with and no comments on the New Directions conference. "It is a group of Democrats with a point of view, and they are meeting," Michael said.

Harrington said the participation of the 10 unions, which represent about 5 million members and historically provide much of the Democrats' money and manpower, reflects organized labor's awareness that combating right-wing economic and social programs has become a "life-and-death question" for a declining American labor movement.

"This is very, very good sign that the labor movement understands it has to innovate or die," he said. The AFL-CIO has not endorsed or participated in the conference, but the 10 participants include some of the labor federation's largest unions.

Most of the $50,000 cost of the conference was paid by the unions, including the United Auto Workers, the United Steelworkers, the Communications Workers of America, the International Association of Machinists, the American Federation of State, County and Municipal Employees and the Service Employees International Union, the Amalgamated Clothing and Textile Workers, the American Federation of Government Employees, the Bricklayers union, and the United Farmworkers.

Much of the conference will focus on economic and tax policy, because Democrats have "lost the idea of truly progressive taxation," Harrington said. He said Democrats must insist that corporate tax breaks be limited to companies that create new jobs instead of "giving away the Treasury in the hope of job creation," which he said was the mistaken rationale of the Reagan administration's tax program.