US Senator Scott Brown casts himself as representing a rare species, one of the ­dying breed of independent Republican senators who seek to broker peace in a ­divided Washington, in the tradition of Leverett Saltonstall, Henry Cabot Lodge II, and Edward W. Brooke, ­Republicans who represented Massachusetts in the Senate.

Warren is channeling the late Senator Edward M. ­Kennedy’s passion for championing the powerless, promising to be a leader in the Democratic majority her election would help secure, fighting harder than Brown ever would against a system now rigged for the wealthy.

“It is a kind of an endless loop in classic Massachusetts political history over the last century,’’ said Thomas J. Whalen, a political historian at Boston University who wrote a book about John F. Kennedy’s 1952 defeat of Lodge, the Brahmin Republican. That race launched the Kennedy dynasty and gave newfound respectability to the Boston Irish political ­establishment, creating the modern coalition that is now backing Warren, a Harvard Law School professor. “This is like Kennedy versus Lodge, in many ways,’’ Whalen said.

But while Warren and Brown’s evocations of older ­political generations may resonate with like-minded voters here, the meaning of what they promise to bring to a profoundly divided Senate and federal establishment is not as clear. Moderates in Congress are rare and getting rarer, and unvarnished liberals can find their causes have little traction in an ideologically charged arena.

On the trail, Warren often speaks reverently of Kennedy, painting Brown as an unfit replace­ment who is out of step with the late senator’s values.

Brown, who also offers a nod of respect to Kennedy, more ­often invokes figures like Brooke and moderate Republican governor William F. Weld.

Political scientists, historians, and average voters wonder whether Brown’s departures from his party’s orthodoxy are really as bold as he says or are true to the values of the silk-stocking Republicans who dominated the state GOP in the mid-20th century with their blend of fiscal probity and ­social liberalism. Brown has joined Republicans around the country in signing, for example, a no-new-taxes pledge that has often been cited as an obstacle to a bipartisan budget deal that could trim the deficit. While he favors abortion rights, antiabortion groups back him.

They also question whether Warren’s strict adherence to liberal values could leave her unable to build consensus in the mode of Kennedy, who learned how to legislate over 4½ ­decades, before the Senate ­became fully polarized.

Warren has indicated that she would have opposed, for ­example, President Obama’s deal with Republicans to ­extend the Bush-era tax cuts in exchange for extending un­employment benefits in ­December 2010. Kennedy, by contrast, forged deal after deal by swallowing something he did not like to get something he loved into law. He always seemed able to find a GOP ally.

“Brown has failed to establish himself in the Senate as a powerful moderate. . . . He hasn’t reached that level of statesmanship that people associate with Saltonstall,’’ said ­Jeffrey M. Berry, a Tufts University political science professor.

As for Warren, Berry said, “my guess is that [she] would embrace full-throttled values of modern liberalism.’’

John W. Sears, one of the last survivors of the generation of patrician political figures, said Brown — though in no way a patrician, with the pickup truck and the hard-luck childhood — can claim some of the mantle the old guard passed on to him and to other moderate state Republicans.

“On the whole, Scott has been more imaginative than most current Republican senators, but he is still right-center,’’ said the 81-year old Sears, a liberal Republican who, despite what he says are Brown’s rightward leanings, still plans to vote for him.

Brown, who voted with the Democrats on financial regulation and on repealing the military’s ban on gays serving openly, is often ranked among the most bipartisan members of Congress.