WASHINGTON — Democratic Sen. Jack Reed finally has a reelection race, but his Republican opponent, Robert Tingle, does not yet promise the kind of political show that Rhode Islanders enjoyed two years ago in Sen. Lincoln D. Chafee’s campaign — with well-financed and well-known opponents, a hard-fought primary and his eventual loss to Sheldon Whitehouse.

But elsewhere, this year’s struggle for partisan advantage in the Senate has plenty of drama in store, with a vivid presidential clash as a backdrop, a pair of interesting New England campaigns and the possibility that Democrats can expand their thin majority.

The Cook Political Report, an independent campaign tracker based in Washington, estimates that the Democrats could add between four and seven seats to their 51-49 Senate majority. (There are two independent senators, Bernard Sanders of Vermont and Joseph I. Lieberman of Connecticut, but both caucus with the Democrats and voted in this Congress for Democratic leadership.)

By all accounts, this year’s political climate favors the Democrats, who are running hard to the drumbeat of “change” behind their presidential candidate, Sen. Barack Obama of Illinois. The Republicans are burdened with an unpopular war, a poorly viewed president who has been in office for almost eight years, and a difficult economy — underscored in boldface every time a voter pumps a $4 gallon of gasoline into the tank.

The politico with day-to-day responsibility for supervising the party’s effort to elect Democrats to the Senate is J.B. Poersch, a former Rhode Islander and Reed’s onetime chief of staff.

Poersch cites a number of recent polls that show a generic voter preference for Democrats and a large majority holding the view that the country is on the wrong track.

“That makes for a fairly formidable environment for Democrats,” Poersch said in an interview last week. On top of that, the GOP is defending some seats opened up by the retirement of popular incumbents and some occupied by senators in states that are shifting to the left.

In New England, the party’s bright prospects start with just such a state. New Hampshire Sen. John Sununu is “the most vulnerable incumbent in the country,” said Jennifer Duffy, who analyzes Senate races for the Cook Report. The state has become increasingly hospitable to Democrats with economic development and the influx of more cosmopolitan immigrants from other states, especially Massachusetts. The question this campaign will answer is whether “the state has changed so much that Sununu is now just too conservative,” said Duffy.

Sununu, whose father and namesake was a New Hampshire governor and chief of staff to President George H.W. Bush, faces Jeanne Shaheen, a former Democratic governor.

Next door in Maine, there was some early speculation that Sen. Susan Collins might be this year’s Linc Chafee — that is, a vulnerable Republican moderate in a Democratic state. Collins faces Rep. Tom Allen, who represents the more populous of Maine’s two congressional districts. But the evidence of the polling and fundraising trends so far does not appear to put Collins among the GOP’s most vulnerable.

For Democrats, the marquee race on the Eastern seaboard is in Virginia, where the retirement of an institution, Sen. John W. Warner, has put his party at a disadvantage in a battle of the former governors, middle-of-the-road Democrat Mark Warner (no relation) and conservative Republican Jim Gilmore. Warner was the more popular (and recent) chief executive, but Gilmore may have bigger worries in the Old Dominion’s New Hampshire-like trend to the left.

These days, Northern Virginia is only nominally part of Dixie. The suburbs of Washington have long been home to lots of expatriates in government and the military, but booming defense and high-technology industries have urbanized the region and made it more and more Democratic.

Among the other states widely viewed as up for grabs, two Senate seats are held today by solid GOP incumbents who are stepping down — Colorado’s Wayne Allard and New Mexico’s Pete V. Domenici. Like Virginia, both of these mountain states figure to get a lot of attention from the presidential candidates.

In New Mexico, Democratic Rep. Tom Udall will face Rep. Steve Pearce in a Senate race with one feature that may be familiar to Rhode Islanders. Pearce had the GOP primary backing of the Club for Growth, a conservative organization that supported former Cranston Mayor Steve Laffey in the 2006 Rhode Island Republican primary. The difference is that Pearce won.

Colorado, host to this summer’s Democratic National Convention in Denver, may be this year’s “ultimate swing state,” up and down the ticket, according to Duffy. Colorado’s Democratic Senate candidate is Rep. Mark Udall (brother of Tom); the Republican candidate is former Rep. Bob Shaffer.

Minnesota — St. Paul, specifically — is host to the Republican convention and to the Senate race that just might draw the most national attention. Or if recent headlines are any indication, notoriety. Republican Sen. Norm Coleman has long been considered a vulnerable target for Democrat Al Franken, but the comedian has had a run of bad publicity over the coarse language he used in an article in Playboy magazine.

Rounding out the list of most vulnerable Senate Republicans is Alaska’s Ted Stevens, a legendary champion of home-state federal spending projects who is under federal investigation in connection with expensive renovations to a home he owns.

The most endangered Democratic incumbent is Louisiana Sen. Mary Landrieu, whose narrow margins of previous victories have come from the Democratic stronghold of New Orleans. The city has lost tens of thousands, many of them potential Democratic voters, since Hurricane Katrina.

CORRECTION: A previous version of this story incorrectly identified Rep. Tom Allen, a Maine Democrat.

jmulligan@belo-dc.com