Few signs of life disturb the lonely peace of Yucca Mountain. It juts above the scarred landscape of the Nevada Test Site, overlooking the Funeral Mountains of California's Death Valley and a rocky desert the color of tumbleweed.

The only community of sorts nearby is Amargosa Valley, a town of about 1,600 people spread over 455 square miles where the main attractions are a brothel, a saloon, an opera house and the sight of Yucca Mountain itself.

But all of Nevada cares deeply about the fate of Yucca Mountain, which stands 90 miles west of Las Vegas. Nevada cares so deeply that Yucca Mountain may decide whether President Bush or Sen. John F. Kerry wins the state's five electoral votes on Tuesday -- and with them, perhaps the presidency.

Most Nevadans are dead set against Yucca Mountain becoming the nation's nuclear dump site. In 2000, Bush, who defeated Vice President Al Gore in Nevada by four percentage points, told voters that he would approve Yucca Mountain as a burial ground for 77,000 tons of radioactive waste from 131 sites in 39 states based on "sound science." Bush approved the site in 2002 on the recommendation of the Energy Department -- a move Nevadans have not forgotten.

Not that the Democrats will let anyone here forget. A dizzying number of television ads over the past several weeks from the Kerry campaign, the National Democratic Committee and MoveOn.org all hammer home the point: Kerry is against using Yucca as a nuclear dump, Bush is for it.

And although terrorism, security, the war in Iraq and the economy are the big issues here, in a deadlocked race, pollsters say, Yucca Mountain could tip the balance.

Kerry repeated his promise to keep the nuclear waste away in a rally in Las Vegas on Tuesday. "How many broken promises do you need, Nevada?" Kerry said, adding that Bush promised he would not go forward on Yucca Mountain unless it was safe. "Nevada, not on my watch."

Two of the state's largest newspapers cited Yucca Mountain in endorsing Kerry. The Las Vegas Sun wrote: "President Bush campaigning in Nevada in 2000 masked his true stance on Yucca Mountain. . . . He pushed for Yucca Mountain almost from day one in the White House." The Reno Gazette-Journal used Harry M. Reid, the popular Democratic senator, to vouch for Kerry: "When Kerry says that he will not allow Yucca Mountain to be used as a nuclear waste repository, Reid says that Nevadans can believe him."

The latest polls show the race is a dead heat. A Reno Gazette-Journal/News 4 poll of likely voters released this week showed 49 percent for Bush and 47 percent for Kerry; 2 percent remained undecided, Ralph Nader received 1 percent and other candidates claimed 1 percent. The margin of error was plus or minus four percentage points.

Democrats and Republicans each claim about 40 percent of the electorate, but Clark County, encompassing not only Las Vegas but also booming suburbs such as Henderson, which helped the county become the fastest-growing region in the country in the 1990s, is a Democratic stronghold.

In the Gazette-Journal/News 4 poll, Kerry led Bush in Clark County, with 70 percent of the state's voters, 53 percent to 42 percent. Bush was ahead in Washoe County, the state's other population center, by 10 points, 53 percent to 43 percent.

"Yucca Mountain is what's probably making Kerry competitive in Nevada," said Del Ali, whose firm, Rockville-based Research 2000, conducted the latest poll.

"It's really not so much a Clark County issue since Kerry has to do well there anyway," Ali added. "But if Yucca Mountain pulls Bush's support under 55 percent in Washoe County and other rural parts of the state, Kerry will win."

Early voting, which ends Friday, has been heavy, suggesting a record turnout, according to state election officials. More than 200,000 people in Clark County had cast their ballots as of Wednesday, with Democrats holding the lead. Both parties say turning out their voters is key, as it is in all the swing states, and they have huge get-out-the-vote efforts underway, climaxing this weekend when thousands of volunteers are set to blanket the state.

Bush, like Kerry, campaigned in Nevada this week, and both are scheduled to bring in big-gun surrogates for the final lap of the race. Former president Bill Clinton, who carried Nevada twice, is to headline a rally Friday in Las Vegas. Vice President Cheney will be in Reno and parts of Clark County on Monday.

In 2002, President Bush approved Yucca Mountain as the burial site for 77,000 tons of radioactive waste.