Washington ? Public anxiety over mounting casualties in Iraq and doubts about long-term consequences of the war continue to rise and have helped to erase President Bush’s once-formidable advantage over Sen. John F. Kerry concerning who is best able to deal with terrorist threats, according to a new Washington Post-ABC News poll.

Exactly half the country now approves of the way Bush is managing the U.S. war on terrorism, down 13 percentage points since April, according to the poll.

Barely two months ago, Bush comfortably led Kerry, the presumptive Democratic nominee, by 21 points when voters were asked which man they trusted to deal with the terrorist threat. Today the country is evenly divided, with 48 percent preferring Kerry and 47 percent favoring Bush.

The shift is potentially significant because Bush has consistently received higher marks on fighting terrorism than on Iraq, and if the decline signals a permanent loss of confidence in his handling of the campaign against terrorism, that could undermine a central part of Bush’s re-election campaign.

Overall the poll had mixed news for both candidates. Bush’s marks for handling the economy and Iraq both rose slightly over the past month, but his overall approval rating remains below 50 percent. Kerry leads Bush in a three-way test that includes independent Ralph Nader and is seen as more honest and trustworthy than the president, but those surveyed question whether he has his own plan for Iraq.

Fewer than half of those surveyed — 47 percent — say the war in Iraq was worth fighting, while 52 percent say it was not, the highest level of disapproval recorded in Post-ABC News polls. Seven in 10 Americans now say there has been an “unacceptable” level of casualties in Iraq, up six points from April and also a new high in Post-ABC News polling. The American death toll in Iraq reached 837 Monday.

A majority say the United States should keep its forces in Iraq until the country is stabilized, but the proportion who want to withdraw now to avoid further casualties — 42 percent — has inched up again to a new high.

A total of 1,201 randomly selected adults, including 1,015 self-described registered voters, were interviewed June 17 to 20 for this telephone survey. The margin of sampling error for the overall results is plus or minus 3 percentage points.