By Bob Benenson, CQ Staff

There’s nothing like the six-seat gain in 2006 that boosted the Democrats into majority control of the U.S. Senate to give the party faithful visions of grandeur. This was embodied in the announcement earlier this week by MoveOn.org — a Web-based liberal activist group most closely identified with presidential politics and issue campaigns — that it is going to put significant resources into helping the Democrats achieve a “filibuster-proof” Senate majority of 60 seats.

Since the Democrats currently enjoyed only a razor-thin operational majority of 51 seats, the goal set by MoveOn would require — yikes! — a nine-seat net gain by the Democrats in this November’s elections.

That is a lofty goal indeed, considering that the Democrats’ six-seat pickup in the last round of Senate elections was the biggest for either party since the eight-seat gain in the 1994 elections that put the Republicans into the majority. You have to go back to 1980, when Republicans rode the coattails of presidential victor Ronald Reagan to a 12-seat gain and a Senate majority, to find the kind of numbers Democrats are now talking about in their muscle-flexing moments.

A party needs at least 60 seats (assuming all its members toe the party line) to ensure the three-fifths majority needed to cut off the filibusters allowed under Senate rules and proceed to floor votes on legislation. The last time either party won enough Senate seats to break filibusters on its own was in 1976, when the Democrats — still in their long period of congressional domination dating to President Franklin D. Roosevelt’s New Deal of the 1930s — ended up with 62 seats.

That doesn’t, however, necessarily mean that the big gain targeted by Democratic officials and groups such as MoveOn is a pipe dream. One of the extraordinary facets of what the Democrats achieved in 2006 was that they had a limited number of serious opportunities to take over Republican-held seats, and they cashed in nearly all of them, including a couple that looked like longshots when the campaign began. By comparison, the Democrats this year enjoy a virtual all-you-can-eat buffet of opportunities to capture GOP seats and extend their majority.

The Republican headaches start with the fact that this happens to be an election cycle in which their party has many more seats at stake. While the Democrats are defending just 12 seats in November, the Republicans have 23 seats in play (including those of two interim senators, Roger Wicker of Mississippi and John A. Barrasso of Wyoming, who were appointed last year to fill vacant seats and face special elections in November to fill out the remaining unexpired terms of their predecessors).

The GOP’s degree of difficulty was greatly heightened by the decision of five of its incumbents to not seek re-election this year. Three of those departing members, John W. Warner of Virginia, Pete V. Domenici of New Mexico and Wayne Allard of Colorado, left open seats that are rated by CQ Politics as highly vulnerable to Democratic takeover. Meanwhile, all 12 of the Democratic Senate incumbents whose seats are up for election this year are running for re-election, and only one — two-term Sen. Mary L. Landrieu , whose race is rated Leans Democratic — is viewed as being in any significant danger.

Overall, CQ Politics currently rates the Democrats as highly likely to pick up the open seat in Virginia, for which popular Democratic former Gov. Mark Warner has established himself as a solid favorite to succeed retiring five-term Republican incumbent Warner (no relation). Domenici’s seat is rated as leaning Democratic, with the party’s rallying around five-term Rep. Tom Udall as their candidate while Republicans brace for what is expected to be a bruising battle between Reps. Steve Pearce and Heather A. Wilson in the campaign for the June 3 primary.

There are three contests for Republican seats that are currently rated as toss-ups, meaning the Democrats’ odds of converting them to their column are about even. The Democrats have strong contenders in each of those races, and all of them are in swing states where the party did quite well in the 2006 elections: Colorado, where Democratic Rep. Mark Udall and Republican former Rep. Bob Schaffer are competing for Allard’s open seat; Minnesota, where entertainer and longtime Democratic activist Al Franken appears the likely challenger to first-term senator Norm Coleman ; and New Hampshire, where Democrats succeeding in recruiting former Gov. Jeanne Shaheen for a rematch of the close 2002 race that she lost to Republican John E. Sununu .

That’s five seats, a big step towards nine, but it assumes the Democrats run the table on their best shots just as they did in 2006. That’s hard enough to do once, no less twice in a row.

And, to get close to nine, the Democrats likely have to sweep the three races for GOP seats that are now rated as highly competitive but leaning to the Republicans. They include the race in Alaska, in which CQ Politics just changed the rating on Friday to Leans Republican from Republican Favored.

The Republican incumbent, Ted Stevens , is a fixture in the seat, with his popularity propelled by his efforts as an Appropriations Committee veteran to channel huge amounts of federal money to his home state. But publicity over a pending federal investigation into Stevens’ ties to business executives who are embroiled in a massive state political corruption scandal places him in an unusually volatile political environment, and it looks increasingly likely that the Democrats’ most-sought-after candidate, Anchorage Mayor Mark Begich, will enter the race.

The other Leans Republican contests are in Oregon and Maine, where a pair of two-term incumbents, Gordon Smith and Susan Collins respectively, are defending for the Republicans. They hold seats in a couple more swing states where Democrats have generally prevailed in recent elections, but both have strong bases of popular support based on their images as relatively moderate Republicans.

But say the Democrats sweep even these three races. That still only gets them to eight, one short of what they need to get to 60. To get over the top, they would need to score a longshot victory or two.

Democrats contend they have realistic chances against Kentucky’s Mitch McConnell, who they portrayed as carrying water in his role as Senate minority leader for unpopular policies of President Bush; North Carolina’s Elizabeth Dole ; Wicker in his first defense of his new Mississippi seat ; and John Cornyn of Texas. But all these contests are in the South, which remains by far the Democrats’ most difficult region, even after their recent gains. It’s also the region where Louisiana’s Landrieu is the Democrat most at risk of losing a seat held by the party.

Still, it makes sense for the Democrats and their allies to aim as high as they are aiming. Even a five- or six-seat gain would get them to the upper 50s. And if they were to get to that point, they would be within range of breaking filibusters at least on some of their priority issues — albeit by persuading some of the handful of surviving moderate Republican senators to vote with them.