For a campaign manager, it was like winning the lottery.

In late January, Jim Rassman, a Republican and a retired police officer, called the office of Democratic presidential candidate John F. Kerry to see if there was anything he could do to help. Thirty-five years earlier, Kerry had won a Bronze Star for helping to pluck a wounded Rassman from the Bay Hap River while under Viet Cong fire.

Rassman and the Massachusetts senator met at an emotional reunion in Des Moines on the final weekend before the Iowa caucuses. The dramatic moment added to the last-minute momentum that brought Kerry a come-from-behind victory in Iowa and set him on the path toward his party's nomination for president.

The Rassman-Kerry reunion also signaled the determination of both Kerry and President Bush to compete for the votes of veterans, a constituency traditionally considered more Republican than Democratic.

The battle for veterans hearts and minds is likely to be crucial given this year's closely divided electorate. But it also serves as a metaphor for the larger national security issues paramount in the minds of all voters in a time of war and terrorism.

Both campaigns have organized extensive grass-roots networks aimed at veterans, and their efforts will be highlighted this weekend as they build appearances around the traditional rites of Memorial Day.

Bush, whose role as commander-in-chief was on display last week as he spoke about Iraq at the U.S. Army War College in Carlisle, will continue to talk about the contributions of veterans as he travels to Europe this week to commemorate the 60th anniversary of D-Day.

Kerry chose the period between Memorial Day and D-Day for a series of speeches and events focusing on national security issues. On Friday in Minneapolis, Kerry will appear with veterans from across the country to try to beef up his Veterans for Kerry organization.

Both sides have enlisted celebrity vets.

In conference calls for reporters, the Bush campaign has featured Scott O'Grady, the Air Force fighter pilot who was dramatically rescued after being shot down over Bosnia, and Mike Durant, the Black Hawk helicopter pilot captured by insurgents in Somalia during the harrowing encounter described in the movie and book, "Black Hawk Down."

Kerry is being accompanied this Memorial Day weekend by Erie resident Joseph Lesniewski, a World War II veteran of the 101st Airborne Division's Easy Company, the "Band of Brothers" depicted in the Stephen Ambrose book that became an HBO mini-series.

Veterans make up nearly 13 percent of the voting age population, and scholars who have studied their voting behavior say that while they often favor Republicans, they are anything but monolithic when it comes to politics.

Professor Larry J. Sabato, director of the Center for Politics at the University of Virginia, has written on veterans preferences in presidential elections. The sometimes "squishy" data available, he said, suggest that majorities of veterans voted for Republican candidates in most of the presidential elections of the last few decades, including President Bush in 2000. He noted exceptions, however, such as in 1964 when veterans acted much as the rest of the electorate in providing a Democratic landslide for Lyndon Johnson.

"I think it is fair to suggest that veterans tend to be a bit more Republican," Sabato said, "but contrary to popular belief, they are not overwhelmingly Republican."

A recent Gallup poll supports that observation.

The national survey, conducted May 7-9, found that veterans were more inclined than all registered voters to support Bush, but only by a narrow margin. Kerry led Bush 50 percent to 46 percent among all registered voters, while a subsample of veterans favored the president 51 percent to 46 percent.

The margin of error of plus or minus 4 percentage points for subgroups is substantially larger than the poll's overall margin , so the survey suggests the preferences of veterans differ little, if at all, from those of voters at large.

"I would argue that veterans are more generational than partisan," Sabato said in an e-mail exchange.

More recent veterans and currently serving members of the armed forces tend more to the Republican camp, although the data is not conclusive, Sabato said.

In the 2000 Census, the nation's 8.4 million Vietnam-era veterans accounted for the largest share of living veterans. The next largest group, nearly six decades after their war ended, are World War II veterans, who number 5.7 million. There are 4 million living Korean War veterans and roughly 4.4 million who served in the years between the Korean and Vietnam conflicts. An additional 3 million veterans have served since 1990, which includes service in the first Gulf War.

While veterans account for 12.7 percent of the voting age population, they make up slightly larger shares of potential voters in several key battleground states, including Pennsylvania, Ohio, West Virginia, Florida, Missouri and Wisconsin. Three of the ten cities with the largest proportions of veterans are in Florida, which is both a retiree haven and an address of convenience for many members of the armed forces because it has no income tax.

For veterans, as for the general population, the chief national-security argument made by Bush and Kerry for their candidacies is that they would be the better commander-in-chief at a time of international peril.

Kerry highlights his own experiences as a decorated soldier in Vietnam and often surrounds himself with fellow veterans.

"These are the band of brothers I relied on 35 years ago," Kerry told students at the University of South Carolina in the days before that state's primary. "We are a little older, a little grayer, but we still know how to fight for our country."

Appearing with Kerry, as on many subsequent stops, was former Georgia Sen. Max Cleland, who contrasted Kerry's Vietnam service with Bush's stateside tour in the National Guard. As in past elections, Bush has had to fend off questions about whether he performed all of his required service during his Guard years.

Bush allies have sought to put Kerry on the defensive on Vietnam-era issues, as well. While fellow swift boat veterans have spoken of Kerry's valor, other swift boat vets have organized to protest his subsequent anti-war activities.

Earlier this month, a group of Vietnam veterans held a news conference to assail Kerry's fitness to be commander-in-chief. Kerry aides dismissed the group as a concoction of the Bush campaign, a charge that its members denied, insisting that their actions were totally independent.

Beyond the broader concerns of war and peace, Kerry and Bush differ on issues more specific to veterans and the organizations that represent them.

Kerry has endorsed veterans organization calls to end the practice of deducting veterans' disability payments from military retirement checks, an issue of intense interest to many veterans. And in an ambitious proposal at a time of looming budget deficits, Kerry also would expand access to Veterans Administration health care.

Currently, while any veteran with a service-connected health problem is eligible for care, some with relatively higher incomes or with ailments or disabilities that are not service-related are not. At a cost of scores of billions of dollars, Kerry would make the veterans health system available to all veterans, transforming it into an entitlement program like Social Security or Medicare.

Kerry and other Democrats have frequently denounced the Bush administration's approach to veterans health care, charging that it has short-changed the system and imposed cuts in health funding. The administration denies the charge, pointing out that spending for veterans has increased sharply since Bush took office.

An independent watchdog group, FactCheck.org, supports many of the administration's contentions. In a recent report, the organization noted that funding for veterans has gone up twice as fast under Bush as it did during the Clinton administration, while the number of veterans receiving benefits has increased by 27 percent.

That spending pace, while faster than in previous years, has not been sufficient to quell the demands of veterans' organization, who contend that the rationing of health care in the face of rising costs has locked many veterans out of the system. A coalition of veterans groups has asked Congress to increase veterans spending for next year by $3.7 billion above the administration's request.