Meet a friend of mine. He is a successful lawyer who lives in the suburbs of Philadelphia, has two grown children, and has been a registered Republican for almost his entire adult life.

That is, until now. Increasingly disenchanted with the GOP, but no fan of the Democrats, he is thinking about re-registering as an independent when he completes a move to a new suburban home and has to change his place of voting.

My friend has plenty of company. In this starkly partisan era of Red and Blue America, we may need a third color to describe those who formally call themselves neither Republican nor Democrat. When it comes to registering voters, the two major parties can only look in envy -- and dismay -- at the swelling ranks of unaffiliated voters.

Since the waning years of the Reagan administration, or basically since the last periodical cicada mating cycle, the number of "other" voters has proliferated. In the 27 states (plus the District of Columbia) that have been registering voters by party since 1987, the Democratic share has plummeted 8 percentage points, declining from an aggregate total of 51 percent to 43 percent. The Republican share has stayed steady at 33 percent. But the proportion of voters who have not identified themselves with either of the major parties has jumped 8 percentage points, from 16 to 24 percent.

What's impressive about these numbers (at least in the view of political analysts such as me) isn't the phenomenon itself, but its staying power. Myriad polls over the past two decades have shown that voters, when asked to identify themselves politically, divide about one-third Democratic, one-third Republican and one-third independent. But in terms of registration, most have opted for one major party or the other -- perhaps because, in some states, that was the only way they could vote in a party primary. Only recently have registration figures begun to reflect the poll numbers.

What's so significant about the rise of the unaffiliated? Well, it's one thing to tell a pollster that you consider yourself "independent." No particular consequence arises from that self-identification. But to register as unaffiliated is a stronger statement of preference (or lack of one). Political parties talk about the "base," and how to energize it. These numbers suggest that the base is eroding, or at least is harder to identify and rely on.

If that's true, we can expect to see a change in how the major parties conduct their campaigns, particularly in states such as Florida, where the number of registered "others" has quadrupled since 1987 and now comprises 20 percent (1.8 million voters) of the state's electorate. Political strategists from both parties are hard at work trying to figure out the best way to appeal to these voters -- and whether unaffiliated means unhappy (a pox on both your houses) or merely unwilling to be labeled.

It is not easy to get a handle on the unaffiliated movement. The states each have their own registration procedures, and many (including Virginia) do not ask voters to indicate a party preference. Registration data isn't published in any sort of regular way or at any uniform time; figures for this article were compiled by contacting state election offices or culling the data from state Web sites.

Viewed in actual numbers, the total of "other" voters in these 27 states and the District has doubled since 1987, from more than 10 million then to more than 21 million now. (The Democratic ranks have grown by 4.8 million; the Republicans by slightly more than 8 million.) Some of these unaffiliated voters registered with a third party -- such as the Greens or Libertarians. But by and large, when one is talking about "other" voters, one is referring to independents -- aka Unaffiliated, Declined to State, or whatever their nom de plume might be in the states that offer party registration. (For the record, at least two of the remaining 23 states, Utah and Rhode Island, are phasing in party registration. In the others, there is no registration by party or, in the case of North Dakota, no registration at all.)

Understanding the unaffiliated will keep political scientists plenty busy for a long time to come, but we already know they make up a disparate group. Some are one-time Democrats or Republicans, disgruntled with their former party. Some are new voters, not ready to commit to any party or disdainful of people who put a label on their politics. Many are "raging moderates," comfortable with the comparative calm of the political middle. And for some, independent status is simply a matter of a particular state's registration rules.

In New Jersey, for instance, new voters are automatically enrolled as unaffiliated unless they fill out a separate form requesting identification with a particular party. Thus, 56 percent of registered voters are listed in the unaffiliated category, but that's almost certainly not an accurate reflection of their leanings. (New Jersey election officials plan to revise their registration form to make it easier for voters to register with a party.)

Meanwhile, in Alaska, 60 percent of voters are registered outside the two major parties. But that figure is deceptive. They can designate themselves as undeclared -- which in Alaska means they can belong to a party, but do not wish to declare which one. And in Massachusetts and New Hampshire, where the proportion of independents is also high, unaffiliated voters are allowed to participate in either the Democratic or Republican primaries, a freedom of movement that voters registered with one of the major parties do not have.

Despite these quirks, however, the trend line is unmistakable, with the registration figures since the last presidential election being particularly telling. Over the last four years, as election officials have purged their rolls of inactive voters, the Democratic total in the party-registration states has fallen by 1.3 million. The Republicans are down far less, only 170,000 in those states. But the "other" category remains a growth stock, adding more than 600,000 voters since George W. Bush and Al Gore did battle.

In short, both parties will have to work hard in the months ahead to get their base back to where it was on the eve of the 2000 election while dealing with an electorate that is becoming more and more independent in its registration habits.

The ranks of the unaffiliated voter have grown as the country has become more mobile, more suburban and less attached to political parties. Will this movement grow large enough to disrupt the seesaw nature of American politics over the past 100 years?

Through the first half of the 20th century, national politics was dominated first by the Republicans, then -- after the onset of the Depression -- by the Democrats. One party or the other tended to monopolize power as straight-ticket voting was the norm.

After World War II, the country and its politics began to change as a large number of voters relocated from small towns and central cities to new, politically rootless suburbs. Independents emerged as a visible factor, helping trigger a new era of split-ticket voting and divided government. Republicans won the presidency more often than Democrats; Democrats held a nearly unbroken grip on both houses of Congress.

Over the last dozen years, the continued growth in independent voters has helped launch a whole new period in American politics, the basic dynamic of which can be summed up in three words -- expect the unexpected.

In the 1990s, a Democrat won two terms in the White House for the first time in a half-century. But the Republicans broke the Democratic hold on the House and the Senate. Meanwhile, independent and third-party presidential candidates -- of only occasional significance for most of the 20th century -- have regularly tallied millions of votes. And the 2000 election culminated with a historical rarity, an electoral college "misfire." For the first time in more than a century, one candidate won the electoral vote and another took the popular vote.

For the immediate future, the registration trends point to more of the same -- an increasingly untethered electorate that gives party strategists more to worry about than marshaling their base vote.

In terms of registration, the Democrats are on a downward slide, living off the fumes of the New Deal era when they were the nation's majority party. Now, at best, they are the plurality party. Yet the Republicans have not been able to rush into the vacuum. Since the last cicada outbreak, their share of voters in the party-registration states has remained stuck at one-third. Republicans hold a registration advantage in just seven small or mid-sized states (compared to the Democrats' edge in 13, including several of the most populous). All of the "GOP seven" are west of the Mississippi River; Arizona, with 10 electoral votes, is the largest.

Meanwhile, the trend among voters who don't identify with either party is the reverse of that among Democrats. Since 1987, the proportion of unaffiliated voters has grown in every region and every party-registration state but two (Colorado and Kansas). These "other" voters are a plurality in a quartet of New England states (Connecticut, Maine, Massachusetts and New Hampshire), plus New Jersey, Iowa and Alaska. In this year's presidential election, Iowa, Maine and New Hampshire are already considered battleground states.

What might a continued rise in independent voters portend for American politics beyond 2004? One appealing thought is that it might bring increased comity to an electoral process that badly needs it. At least that is what seems to have happened in states such as Maine and Colorado, where the registered electorate has been closely divided for years among Democrats, Republicans and independents.

Candidates in both states employ slash-and-burn tactics at their peril. Rip-roaring partisanship and negative campaigning may be commonplace in much of the country. But in Maine and Colorado, the surest route to victory is to tone down the partisanship and smooth the ideological edges in order to appeal to the broad mass of independents.

Voters in Colorado have quite literally shown that they vote the person rather than the party, electing Ben Nighthorse Campbell to the Senate in 1992 as a Democrat, then electing him to a second term as a Republican. Meanwhile, Maine has elected two independent governors in the last 30 years, one of them for two terms; Olympia J. Snowe, the state's senior senator, is considered one of the most independent-minded Republicans in Congress.

There is little doubt that the rise of the unaffiliated has had a moderating influence on who gets elected in both states. Ted Kennedy Democrats are hard to find in either. So are Tom DeLay Republicans. For those of us who worry about a future defined by the sharp shadings of Red and Blue America, perhaps there is hope in contemplating what might happen if the politics of states such as Maine and Colorado were to go national in the years ahead.

Author's e-mail: rhodescook@aol.com

Rhodes Cook analyzes political trends at RhodesCook.com and publishes a bimonthly newsletter. He is co-author of "America Votes," Congressional Quarterly's biennial summary of national election results.