For all the new talk of civic activism, today's most powerful American -- at least as far as Washington is concerned -- may well be the uninvolved citizen. For it's his or her disengagement from national politics that drives the method of governance at the margins.

Those citizens -- complacent, disgruntled, alienated or apathetic -- who figure it doesn't matter what they think, that the government won't be responsive to them anyway, are in fact powerfully shaping government. Their absence leaves the middle ground thinly populated. And today's policymaking by the extremes thrives on their lack of interest.

I plant this thought into a field of vigorous debate about citizenship in America. What does it take to be a good citizen? Voting? Activism? Staying informed? There is considerable optimism lately that the activism part, at least, is looking quite robust.

It was Robert Putnam's 1995 essay, "Bowling Alone: America's Declining Social Capital," that kicked off this debate in earnest. The Harvard political scientist argued that Americans were fast abandoning public life, with participation in groups spiraling downward everywhere.

Putnam's thesis sparked lively disagreement, and the latest popular notion is that today's Americans are, on the contrary, great joiners. Everett Carll Ladd, executive director of the Roper Center for Public Opinion Research at the University of Connecticut, told The Post recently that America is witnessing an "explosion of voluntary groups, activities and charitable donations [that] is transforming our towns and cities."

Similarly, a recent article in the New York Times focused on the new world of citizens flexing their social muscles and "reshaping politics and economics both at the domestic and global levels," in the words of Lester M. Salamon, director of the Center for Civil Society Studies at Johns Hopkins University. "I believe it is as important a development to the latter part of the 20th century as the rise of the nation-state was at the end of the 19th century," he said.

With all this participation, some question how much it matters that so many Americans don't vote. "The low rate of voting in the United States often leads to the misconception that Americans are a relatively inactive and apathetic people," wrote Jeffrey M. Berry in his recent book, "The New Liberalism: The Rising Power of Citizen Groups."

"Discouraging as it might be, Americans' lack of enthusiasm for voting is a misleading indicator of their overall involvement in community and political affairs. Americans are very generous in volunteering time to charities, community organizations, churches, schools and other civic-minded groups."

Still, I wonder: All this activism does not seem to have made itself adequately felt in Congress. Meanwhile, the lack of voting has. American voter turnout is dramatically lower than that of most advanced nations. Fewer than half of Americans of voting age went to the polls in 1996, a presidential election.

With the moderating voice of the thoughtful middle dwindling, polarization reigns, and interests at the edges of public opinion dominate. In such an atmosphere, it is hard to govern thoughtfully, with an eye on the broad public good.

Former member of Congress David Skaggs, speaking recently at the Woodrow Wilson Center, said, "The falloff in participation of people in political life has an effect on the way members of Congress behave."

Peeling away the layers of low voter participation's impact on Capitol Hill, Skaggs said, "The majority in the House reflects the view of some 17 percent of the American people. The majority within that majority that controls the agendas . . . runs at 12 or 13 percent. Both parties put their most ardent partisans on the Judiciary Committee -- reflecting the views of maybe 8 or 9 percent." And in such settings are critical decisions made.

Representatives feel compelled to act in ways that are "really acceptable to that 12 to 13 percent that got you where you are" -- a situation that is easily "leveraged by those extremes within the political spectrum."

It is also a situation that is self-perpetuating, Skaggs added: "The more extreme it all appears, the less motivated people are to participate."

This power at the margins must be a factor in the rupture between people and government. The number who say they trust the government to do what is right has been cut in half in the past generation; it's now 31 percent. A Congress beholden to extremes can't patch things up.

"Bowling alone" may be inaccurate. Even so, it's hard to be too relieved, when "voting alone" comes so close to the truth.