WASHINGTON -- Iraq is likely to be the "trump card" that most sways swing voters in the presidential election, which will be generally determined more by foreign policy and national security issues than at any time since the 1970s, according to a poll released yesterday by the Pew Research Center for the People and the Press and the Council on Foreign Relations.

"Barring a sizable shift in public opinion over the next few months, the 2004 election will be the first since the Vietnam era in which foreign affairs and national security issues are a higher priority than the economy," according to the center's analysis of the survey data.

Like much of the electorate, swing voters in battleground states -- such as Ohio, Florida, Pennsylvania, Michigan, Missouri, Wisconsin and Iowa -- are split over which candidate is stronger on foreign policy and the war on terrorism. Swing voters come closer to Democrats on foreign policy, but closer to the Republican position on combating terrorism, on which Bush gets "strong marks," the poll found.

So the pivotal issue is Iraq, and swing voters are closer to the Democrats on Iraq, the survey concluded.

On eight of 11 foreign policy issues in the poll, "opinions of swing voters are closer to those of Kerry supporters than to those of Bush voters," said the Pew center's analysis.

In a separate commentary on the poll, the Council on Foreign Relations said swing voters are "more likely to see blue than red."

The poll was conducted among 2,009 adults from July 8-18, with an update on Iraq conducted Aug. 5-10 among 1,512 adults. The margin of error was plus or minus 2.5 percentage points for the entire survey and 3.5 percentage points for questions based on answers from just one of the two survey periods.

More than a month after the transfer of political power from the U.S.-led occupation to an interim Iraqi government, the poll found that just over half of American voters surveyed (52 percent) disapprove of the president's management of Iraq policy. And almost 6 of 10 adults (58 percent) said the Bush administration does not have a "clear plan" for bringing Iraq to a "successful conclusion."

"Dissatisfaction with Iraq is shaping opinions about foreign policy as much, if not more than, Americans' continuing concerns over terrorism," said the survey analysis. "Continuing discontent with the way things are going in Iraq underlies public criticism of the Bush administration's overall approach to national security."

The survey also found a "sharp increase" in the number of Americans who have doubts about whether the Iraq campaign has helped curtail the war on terrorism.

Only 45 percent say it has helped, down from 62 percent in February.

Six in 10 Americans (59 percent) believe Bush has been "too quick" in wielding military force, while only a third now say Bush made sufficient attempts to achieve diplomatic solutions before the Iraq war. Yet Massachusetts Sen. John F. Kerry, Bush's Democratic presidential challenger, has not yet convinced swing voters that he provides a viable alternative vision, the poll found.

"Iraq could be the tipping point. But even though things are bad in Iraq, and the public evaluates President Bush poorly on Iraq, Kerry hasn't made the sale on Iraq either," Andrew Kohut, director of the Pew Research Center, said in an interview.