Rep. Shelley Berkley (D-Nev.) listens to Lilly Ledbetter, Sen. Barbara Mikulski (D-Md.) and Senate Majority Leader Harry Reid (D-Nev.) speak before a Senate vote on the Paycheck Fairness Act on June 5. (Bill Clark/CQ ROLL CALL)

— Just two years after fending off one of the nation’s toughest Republican challenges to win reelection to a fifth term, Senate Majority Leader Harry M. Reid could find his political fate determined once again by voters in his own Nevada back yard.

Reid won’t be on the ballot in November. But as the Democratic leader fights to retain his majority in the Senate, with control likely coming down to just a handful of key contests, the Silver State offers a rare opportunity for a Democratic pickup in a year when the party is mostly playing defense.

So the soft-spoken, hard-knuckled Reid is now activating the vaunted Nevada Democratic machine he has helped build on behalf Rep. Shelley Berkley. The seven-term Las Vegas congresswoman is challenging Reid’s junior partner, Republican Sen. Dean Heller, for his job.

Heller and Berkley are both expected to breeze through Tuesday primaries. Then the general election will begin in earnest, pitting Heller against Berkley — and, only slightly less publicly, against Reid himself.

“He’s kind of like the godfather here,” said Chuck Muth, a Nevada political operative who works with conservative candidates. “If Harry Reid says ‘Shelley Berkley is important to me,’ then everyone knows that Shelley Berkley better be important to them.”

Getting an early start

This month, a PAC run by a former Reid spokesman began airing anti-Heller television ads in the key swing Reno area. That mimicked Reid’s own strategy in 2010, when he left some of the race’s most bitter attacks against opponent Sharron Angle to the same group.

Reid also sent top aide Zac Petkanas to the Nevada Democratic Party, where he’s coordinating efforts for Berkley and the Obama campaign in the state, as well as other Democratic races.

Reid has raised campaign cash on Berkley’s behalf, arguing that the path to retaining his spot atop a majority party might run through Nevada.

Petkanas said Berkley is running her own campaign. But he acknowledged the close ties and the importance of the race for Reid.

“We’re proud of the fact that, unlike the Republicans, we can work together,” he said.

Stressing a clear choice

An affable onetime stock broker and former House member, Heller, 52, was appointed to the Senate in 2011 by Republican Gov. Brian Sandoval to replace Sen. John Ensign, who resigned after having an affair with a married staffer.

Heller said he and Reid have a good working relationship. Twenty years Reid’s junior, Heller attended the same Mormon temple as the Reid family as a child and still plays in the same basketball league as Reid’s son Leif.

“I don’t hold any ill will toward his involvement,” Heller said, noting he makes the same case to supporters — that the Senate majority is on the line.

“I think it’s a reasonable argument to make. . . . The stakes are high,” he said.

Berkley too has long ties with Reid, whom she first met in 1968, when she was a high school senior and volunteered on his campaign for state assembly.

She insisted voters this year will have a straight-up choice, deciding who would do a better job protecting the middle class in a state hit especially hard by the economic crash.

“This is a clear choice between Dean Heller and Shelley Berkley, and the voters are going to have that clear choice in November — who’s going to stand for them, who’s going to work for them, who has their interests at heart,” she said.

Republicans need to win at least four seats to take the Senate. They have a number of strong opportunities in Missouri, North Dakota, Montana and Virginia. But if Democrats could seize even one seat from the GOP, it could thwart the Republican advance.

Their best chances for a a possible offensive victory now appear to be in Maine, Massachusetts — and Nevada.

Building a Democratic edge

The reasons for Democratic hope are clear. The state is rapidly diversifying — exit polls showed its electorate was more than 15 percent Hispanic in 2010 and 2008, a group with whom Democrats are far ahead.

Over the past two election cycles, Democrats have built a dramatic voter registration edge over Republicans, an advantage that has dipped somewhat since the 2008 race but remains wide.

And Democrats bring to bear a powerful grass-roots effort that includes intensive Latino outreach and well-organized unions. It worked for Reid two years ago in an otherwise lousy year for Democrats and, more impressively, for President Obama in 2008, when he carried Nevada by more than 12 points.

“The biggest thing Reid has done is to build the Democratic Party to a point where it can be all in for Shelley Berkley,” Petkanas said.

Berkley is also a feisty and hardworking candidate, a lawyer and former Vegas Keno runner who has built a power base in the key left-leaning stronghold of Clark County, which could help her run up the Democratic vote tally.

A late May poll from NBC/Marist showed a dead heat, with Heller leading Berkley by just two points among registered voters, well within the poll’s margin of error. Berkley held strong leads with independent voters and Hispanics.

But Republicans believe that the ground is shifting in Nevada. They believe that the desperately ailing economy — the unemployment rate is 11.7 percent and about 60 percent of homeowners are underwater on their mortgages — means Obama’s edge has eroded.

Berkley could also take a hit in July, when a House ethics panel is expected to announce the results of an investigation into whether she improperly used her influence to block federal regulators trying to close Las Vegas’s only kidney transplant center, where her husband, a physician, held a contract.

She has denied wrongdoing, saying constituents would have been hurt had the program been shuttered.

Republicans point out that the Reid machine has not always been successful, either, failing, for instance, to help elect Harry Reid’s son, Rory, in the 2010 governor’s race.

And Reid also remains a polarizing figure in the state. His involvement could arouse the Republican base and Heller said it could persuade some independents voting for Obama to split their ticket to provide balance.

“I believe at the end of the day it gives me an incredible independence that most Nevadans frankly want you to have anyway,” Heller said.

Reid has embraced Berkley, including at the state party’s convention Saturday. But, a master behind-the-scenes operator, he speaks about the race only rarely and mostly allows his views to be known in more subtle ways.

Last week, Reid engineered a bound-to-fail election-year vote on a perennial Democratic initiative, the Paycheck Fairness Act, designed to help close the pay gap between men and women.

The move was intended to box in Republicans facing tough reelection battles like Heller and was particularly tricky for male senators like Heller facing female opponents.

On the day of the vote, Heller was the only Republican to come to the Senate floor to explain his opposition and outline an alternative he said would curb the frivolous lawsuits he believed the Democratic measure would invite.

Asked about Heller’s speech at a news conference afterward, Reid paused. Then, with Berkley and other female House members hovering just over his shoulder, he displayed a bit of vintage mild-mannered amusement at Heller’s predicament.

“All you people who do print stuff,” he said, “recognize the smile on my face. I like Dean Heller. I like him a lot. Known him for years. . . . With all due respect to my friend Dean Heller, he would have been better off had he said nothing.”

Reid’s wealth of resources

What Reid can really bring to bear for Berkley is his longevity. Over more than 40 years in Nevada politics, he has built relationships with everybody who’s everybody in the state — and a lot of people who aren’t.

Four years ago, Las Vegas paralegal Shannon Jory, 44, voted for Obama. This year she’s an undecided presidential voter, depressed that neither party seems to be taking the state’s housing woes seriously.

But if Reid urges a vote for Berkley in the Senate race, she said, she’d likely follow his advice. After all, she feels a connection to Reid, who used to call her father from time to time — a retired Navy captain who ran a Vegas pawn shop — to ask his advice on military matters.

“There’s a lot of people just like us here,” she said.

Polling analyst Peyton Craighill contributed to this report.