Petra Kelly, a leading force in West Germany's left-wing Green Party, said yesterday that nonviolent civil disobedience and large-scale demonstrations probably will not succeed in blocking the scheduled deployment of NATO missiles in West Germany later this year.

"It's open," Kelly said in reference to the potential for the fall demonstrations to succeed, "but I'm pessimistic." In a meeting with Washington Post editors and reporters, Kelly--who is a member of parliament--called her party's emphasis on blocking the planned installation of cruise and Pershing II missiles an "absolute priority." An accompanying party representative pointed out that the deployment process, set to begin in December, takes four years and thus the Greens will be protesting throughout that period.

The Green Party is primarily known for its fervent support of conservation and opposition to nuclear weapons. In spring elections, the Greens polled slightly more than 5 percent of the vote, earning 27 parliamentary seats. Their casual style of dress, informal manners and radical politics contrast with Chancellor Helmut Kohl's ruling Christian Democratic-Free Democratic coalition government as well as the main opposition, the Social Democrats.

Currently on a week-long visit to the United States with five other Green Party leaders, Kelly said the West German press concentrated too heavily on a violent demonstration two weeks ago against Vice President Bush, whose motorcade was pelted with rocks and bottles in the town of Krefeld, West Germany. The media "did its very best" to publicize the violence, caused by 100 persons, and to ignore a nearby peaceful demonstration attended by 40,000 protesters, Kelly said. While admitting that the Greens "haven't a miracle solution" to stop the violence, Kelly said, "Our role must be to understand the incredible frustration and resignation, and try to keep up the dialogue."

According to Kelly, 35, who was educated in the United States, a meeting Thursday with middle-level State Department officials failed to yield agreement on such issues as arms and human rights.

Kelly said she has requested meetings with President Reagan and Soviet President Yuri Andropov, but has been turned down. If granted a meeting with Soviet leaders, Kelly said, she would "want them to understand we don't accept their view of deterrence, because they're caught up in the same arms race" as the United States. But she said the Greens "understand" why the Soviet Union rejects Reagan's zero-option proposal to cancel the NATO missile deployment if the Soviets dismantle their SS20 missiles aimed at Europe: The Soviets "are asked to take away all of their land-based missiles and we, on the western side, don't remove one air- or sea-based missile, we just remove what is on paper," she said.