Washington ? Mounting concerns about the war and the sluggish economy have sent President Bush’s popularity plummeting among young adults in the past four months, complicating his bid for re-election and challenging Republicans to increase their efforts to win over new or lightly committed young voters.

Four years ago, network exit polls found that Bush and Democrat Al Gore split the vote of 18- to 29-year-olds, with Gore claiming 48 percent and Bush getting 46 percent — the best showing by a Republican presidential candidate in more than a decade.

But that was then. In the latest Post-ABC News poll, taken immediately after the Democratic National Convention, Kerry led Bush 2 to 1 among registered voters younger than 30. Among older voters, the race was virtually tied.

Tyler McLaughlin, 27, of Georgetown, Texas, did not vote four years ago but supported Bush during the first years of his presidency. “But after two years of war, I became anti-Bush,” said McLaughlin, a project scheduler for a computer firm. “This seemed like a guy … who made a decision and won’t go back on it.”

Bush’s problems with younger voters began long before the Democratic convention, Post-ABC polls suggest. The last time Bush and Kerry were tied among the under-30 crowd was in April. In the five surveys since then, Bush has trailed Kerry by an average of 18 percentage points.

Virtually every other major poll conducted in the past month confirms Kerry’s popularity with voters under the age of 30. A poll by the Pew Center for the People & the Press released Thursday reported Kerry still ahead by 18 points among this group.

Taken together, those surveys suggest that if the election took place today, Bush would do about as well among younger voters as GOP presidential candidate Bob Dole in 1996. Dole lost to President Clinton by 53 percent to 34 percent among 18- to 29-year-olds. Bush’s father split the young vote in 1988 and lost to Clinton by nine points in 1992. The Reagan era marked the recent high-water mark for the GOP with younger voters, who gave the Gipper his biggest victory margin of any age group in 1984.

The latest Post-ABC News survey found that Kerry consistently topped Bush by double-digit margins as the candidate young adults trusted to deal with every major issue, including the economy, Iraq, education and health care.