George Allen and Timothy M. Kaine are locked in a dead heat 18 months from Election Day, according to a new Washington Post poll, suggesting that the U.S. Senate race between the Virginia titans may live up to its billing as one of the most competitive contests in the nation.

The candidates are tied at 46 percent among registered voters in the battle to succeed retiring Sen. James Webb (D). Neither Allen (R) nor Kaine (D) is guaranteed his party’s nomination, but the survey shows that both men enjoy huge leads over potential intraparty opponents.

The 2012 contest will play out in a state that has changed dramatically in recent years. Kaine — the former governor and Democratic National Committee chairman — draws strong support in portions of Northern Virginia, which has rapidly gained population, wealth and political clout. Allen, the ex-governor and senator, remains stronger in the rest of the state.

The race may decide which party controls the Senate — a daunting task for Democrats, who must defend 23 seats to Republicans’ 10 next year. And in a state where voters have tossed between Republican and Democratic candidates in recent years, both men must overcome potential vulnerabilities from their pasts: Allen, for the controversial “macaca” incident that helped sink his 2006 Senate campaign, and Kaine for his close identification with President Obama’s policies, which could alienate independents.

Kaine and Allen begin the Senate matchup — which experts say could easily top $30 million — with similarly deep statewide experience, proven fundraising ability and broad name recognition. Both men’s tenure in office is remembered fondly by a majority of Virginians — 58 percent of voters approve of the way Kaine handled his job as governor, while 55 percent approve of Allen’s performance as senator.

Former Virginia governor Tim Kaine (D), left, and former U.S. Senator George Allen (R).

The passage of time has had little effect on their standing. Kaine’s current number matches his job-approval rating in an October 2009 Washington Post survey among likely voters, three months before he left office, while Allen’s rating now is similar to what he received among likely voters in October 2006, a month before he lost his reelection bid.

Fifty-seven percent of voters have a favorable impression of Kaine overall, while 52 percent say the same of Allen.

“It seems that [Allen’s] got a vision, and he follows it to a T,” said Donald S. Brill, 54, a retail store employee from Winchester. “He doesn’t back down.”

Thomas DePriest, 65, a retired federal government lawyer from Falls Church, had a similar opinion of Kaine.

“I think he is an intelligent leader who makes the right decisions,” DePriest said. “I thought he was a good governor.”

But the poll also points to weaknesses in each man’s facade of support. Kaine is trailing among independent voters and in the booming outer suburbs of Northern Virginia, a key battleground in any statewide campaign, while Allen has a steep hill to climb with female and minority voters.

Reason for optimism

Political momentum in Virginia has seesawed over the past decade, giving the parties reason to be optimistic for November 2012.

Republicans hope to continue the trend of 2009, when Robert F. McDonnell won the governorship in convincing fashion, and 2010, when the GOP ousted three incumbent congressional Democrats. Democrats would prefer a repeat of their back-to-back Senate race wins in 2006 and 2008 and another victory for Obama, the first Democratic presidential candidate to win Virginia in more than four decades.

Obama’s presence atop the ticket should boost turnout among blacks, but it’s not clear whether they will vote at the historically high rate they did in 2008. Kaine’s fate could hinge on whether they do: Black voters currently favor Kaine over Allen by a wide margin — 80 percent to 16 percent — while white voters prefer Allen by 19 percentage points.

A gender split is also clear: Allen leads by 12 points among men, while Kaine holds an identical advantage among women. Kaine does particularly well among women younger than 45, while Allen’s strength is with older men.

Virginia’s geographical divide is even more pronounced. In Northern Virginia, voters give Kaine a 21-point advantage. The rest of the state favors Allen by six points.

More specifically, Kaine holds a commanding 27-point lead in the suburbs closest to the District, but Allen leads in the exurban counties — a region that includes Loudoun and Prince William — by 14 points.

Those exurbs are a potential trouble spot for Kaine: He is underperforming there compared with his gubernatorial win in 2005, when he drew 47 percent of the vote. Webb drew the same 47 percent in the exurbs in his 2006 win over Allen.

Kaine is also doing worse than Webb did in the Tidewater region, where 46 percent currently favor Allen and 45 percent favor Kaine.

Kaine, who served as Richmond mayor before becoming governor, does better in the area that includes Richmond and the counties south and east of the capital. Allen trails there by 6 percentage points, even though he beat Webb in that region six years ago.

Each man is drawing about the same level of support from his own party, but Allen leads among independents by 10 points.

As in the rest of the country, Virginia voters are most concerned about economic issues. Allen holds advantages among voters who said the economy, the federal budget deficit or taxes were “extremely important” to their vote. Kaine leads among those who emphasized education.

The Post’s poll was in the field Sunday night when Obama announced that U.S. forces had killed Osama bin Laden in Pakistan. The development appeared to have little effect on Virginians’ Senate choice: Support for Kaine and Allen was similar in interviews before and after the news.

Baggage check

Although relatively popular, Kaine and Allen bring baggage into the race that their opponents hope to exploit.

In 2006, Allen was leading his reelection contest when he referred to an Indian American campaign volunteer for Webb as “macaca,” which is considered an ethnic slur in some countries. Allen’s campaign began to slip amid negative media attention, and he never recovered.

Cindy Lawson, a legal secretary from Alexandria, said she wasn’t “crazy” about Kaine when he was governor but is still leaning toward voting for him in the Senate race because she doesn’t care for Allen — in part because of the “macaca” incident.

“These comments they make off the cuff — that’s your true feelings coming out,” said Lawson, 59.

But most Virginians appear less concerned about the episode. In the new poll, 20 percent of voters say the incident would be “extremely” or “very” important to their vote in 2012, while 78 percent say it will be only “somewhat” or “not at all” important.

Republicans have already begun an assault on Kaine for his service as Obama’s handpicked DNC chairman, painting him as a loyal servant of the president rather than the independent-minded centrist he strove to be as governor.

In the survey, 51 percent of Virginia voters say Obama will not be a factor in their choice for the Senate race, while 26 percent say their Senate vote will be an expression of support for Obama and 21 percent say it will reflect their opposition to the president.

Before Allen gets on the ballot for the general election, he must overcome primary challenges from at least four Republican opponents. The poll suggests that he is well positioned to do so.

In a hypothetical matchup against six other GOP contenders, Allen had the support of 57 percent of Republican voters. Jamie Radtke — the former chairwoman of the Federation of Virginia Tea Party Patriots and most outspoken challenger — took just 2 percent.

Five other declared or potential candidates — Del. Robert G. Marshall (Prince William), Prince William Board of County Supervisors Chairman Corey A. Stewart, Chesapeake Bishop E.W. Jackson, Hampton Roads lawyer David McCormick and Great Falls television production company owner Timothy E. Donner — scored between 1 and 3 percent apiece.

Although Radtke enjoys some support in the tea party community, she is not well known in the state and may need to spend significant cash to boost her profile. While 13 percent of Virginians have a favorable impression of her and 9 percent unfavorable, 79 percent have no opinion.

And although Kaine and Allen are tied, the Democrat holds a 26-point lead among registered voters when matched against Radtke.

Kaine faces no declared primary opposition, but Rep. Robert C. “Bobby” Scott (D) has said he will decide by July whether to run for Senate. Kaine leads Scott among Democratic voters, 67 percent to 17 percent.

The poll was conducted by telephone April 28 to May 4, among a random sample of 1,180 Virginia adults, including 1,040 registered voters and users of both conventional and cellular phones. Results from the registered-voter sample have a margin of sampling error of plus or minus 3.5 percentage points.

Polling director Jon Cohen and staff writers Rosalind S. Helderman and Anita Kumar contributed to this report.