With almost 40,000 troops serving in the unexpectedly violent and difficult occupation of Iraq, the National Guard is beginning to show the strain of duty there, according to interviews and e-mail exchanges with 23 state Guard commanders from California to Maine.

The Iraq mission is placing new stress on the active-duty Army as it leans more heavily than it has in decades on the Guard -- which, with 350,000 troops, rivals the active force in size. That new reliance, in turn, is raising concerns about the Guard's long-term ability to recruit and retain troops, and it is provoking more immediate worries in states that rely on the Guard to deal with fires, floods, hurricanes, tornadoes and earthquakes.

Some Guard commanders are beginning to say they simply can't deploy any more troops. "As far as New Hampshire goes, we're tapped," said Maj. Gen. John E. Blair, that state's adjutant general, or Guard commander. Of his 1,700 Army National Guard troops, more than 1,000 are in Iraq, Afghanistan or Guantanamo Bay, Cuba, or on alert for deployment. And to get units fully manned to head overseas, he said, "we've had to break other units."

Blair, who piloted a medical evacuation helicopter in the Vietnam War, said he informed the Pentagon's National Guard Bureau two weeks ago that "before you call us again, you've got to know that we are at our limit."

Earlier this year, 60 percent of Maine's 2,300 Army Guard troops were deployed. "The current pace isn't sustainable," said the state commander, Brig. Gen. John W. Libby, who said that pace appears to be damaging his efforts to raise manpower. "Our recruiting is down significantly from last year, and our retention rates are down also," he said. The biggest problem, he said, is that parents are discouraging their children from joining. "We've got a level of reluctance with parents this year that we haven't seen in the past."

Some soldiers in West Virginia's 1092nd Engineering Battalion got home in April from 14 months of duty in Iraq -- only to be activated in the past few days for weeks of flood-relief work in Mingo County and other southwestern parts of the state. One soldier told the state commander, Maj. Gen. Allen E. Tackett, that he had been back to his civilian job for exactly one day. "The spouses and the employers are raising hell with me," the general said.

Tackett said he is especially worried that his most seasoned soldiers are getting out. "A lot of my experienced people are coming back from deployments and retiring," he said. "They've paid their dues."

It isn't just the Guard that is feeling the pinch. In Montana, the Guard, facing an alert for deployment, has withdrawn its Black Hawk helicopters from the job of being the first responder to small fires that can flare into forest fires. With that system, "last year, we caught a lot of fires that we wouldn't have otherwise," Montana State Forester Bob Harrington said Friday from his office in Missoula.

Now, with the start of the fire season just a month away, Harrington is scrambling to contract for commercial choppers to fill that quick-reaction job. Their payloads are less than half that of the powerful Black Hawks, which can tote 600 gallons of water.

The last time the U.S. military engaged in sustained ground combat, during the Vietnam War, it could rely on a draft to provide new personnel. Now, lacking conscription, the Pentagon is relying on other tools to find enough soldiers to fight in Iraq and Afghanistan. It has imposed controls such as "stop-loss" to keep active-duty troops from leaving. It has extended the tours of duty in Iraq for some soldiers from a planned year to a possible 15 months. It is reorganizing itself to create more units that can be deployed.

But most of all, it is looking to the Guard. As active-duty troops leave Iraq after tours of a year or more, they are often replaced by Guard troops, with the result that almost one-third of the 125,000 Army troops now in Iraq are from the Guard. Eighty-one Guard soldiers have died in Iraq, 29 of them in the upsurge in violence in April and May. For some states, those were the first combat deaths suffered by the Guard since the Korean War.

Parts of the Guard are beginning to stagger under the burden. Nearly three years into the post-Sept. 11, 2001, world, Guard commanders said they have shed the "weekend warrior" image their force once had. But several said they are deeply worried about how the citizen-soldiers will react to the repeated deployments into combat zones that they now are facing -- and even more about the responses of the families and employers.

Since Sept. 11, North Dakota's Maj. Gen. Michael J. Haugen said, his state has mobilized as many troops as were called up during World War II. Five of the state's Guard members have died in Iraq. While Haugen supports the Iraq mission and his troops like it, he said "we will eventually hit the wall," probably in a couple of years, and be unable to deploy overseas. For certain specialized units, such as engineers, he added, "I'm almost there."

Concerns about the new load being placed on the Guard were aired in mid-May at a meeting in Colorado Springs attended by most of the 54 Guard commanders, who come from all 50 states, Guam, the Virgin Islands, Puerto Rico and the District of Columbia.

Idaho, a small-population state that faces a big fire threat, was kind of a poster child for officers at the meeting. Out of 3,200 people in the Idaho Army Guard, about 2,000 are members of the 116th Cavalry Brigade, which is expected to deploy to Iraq later this year. Their departure poses the question of who will be ready to deal with the state's natural disasters.

Lt. Col. Tim Marsano, a spokesman for the Idaho Guard, said, "I think everybody in the western states is concerned that it could be a very significant fire season." But he said the Idaho Guard is confident that it will have sufficient personnel on hand, in part by tapping members of the Air National Guard if necessary.

Some commanders from the Southeast likewise worry about hurricane season. After a big storm, there is high demand for precisely the sort of troops that have been deployed most heavily -- military police to keep order and engineers to clear debris.

"It's not just how many, it's who, and what kind of skill sets they have," said Maj. Gen. David B. Poythress, Georgia's commander. "When both my MP companies are gone, I don't have any MPs to put on the street."

In Mississippi, the unit designated as "first responders" to repair hurricane damage, the 223rd Engineer Battalion, was deployed for the past year to Iraq. It has come home, said Maj. Gen. Harold A. Cross. But, he added, "they left the equipment in Iraq." He has been told that by hurricane season he will be given the gear belonging to another unit being deployed. He also noted that he has sent 21 helicopters to Iraq, leaving just five for post-storm rescues and transport of cargo and troops.

The brigade the North Carolina Guard now has in Iraq came from the southeastern and southern parts of the state, the area that tends to bear the brunt of hurricanes. "We're a little short people in those areas," said Maj. Gen. William E. Ingram Jr., commander of the North Carolina Guard. In order to ensure that he can serve those areas after a disaster, he said, he will have to mobilize more-distant troops sooner, which will make it more expensive for the state.

As Ingram spoke, he almost seemed to be mentally crossing his fingers. "We're stretched, to a degree, but we're certainly not at the breaking point," he said. "If we can get through this year, we'll be in pretty good shape for next year's hurricane season."

Not all state commanders are sending up the alarm.

"We're an adaptive force," said Florida's Maj. Gen. Douglas Burnett. The new demands, he said, are "just part of the leadership challenge." Even at his peak level of deployment of 5,200 troops, he said, "I could still do about a hurricane and a half" with the remaining 7,000. "You're not going to see me jump up and say, 'We can't do this.' "

Rather, Burnett's complaint is money: "We're proud to be in the fight, but we've got to be funded."

Similarly, Ohio's commander, Maj. Gen. John H. Smith, warned, "We will soon be a hollow force without replenishment dollars to replace what is being consumed or lost."

Commanders from the biggest states generally seem most optimistic. Maj. Gen. Wayne D. Marty of Texas said he expects to send 3,000 soldiers to Iraq later this year. But he has a total force of about 19,000. "We're busy, but we're not stressed," he said. Morale also appears to be high, with reenlistment rates at a 10-year high, he said.

Even so, Marty said, he could see a point when the current pace will no longer be sustainable. "There will be a time when we reach diminishing returns, if this thing keeps going with the op [operational] tempo we have now," he said.

Another big-state commander, Michigan's Maj. Gen. Thomas G. Cutler, also said he saw problems on the horizon. "We're concerned," he said. "Everybody has a certain level of concern about how long-term this will be."

The Pentagon says there are solutions to all the potential shortfalls.

Brig. Gen. Frank Grass, deputy director of the Army National Guard, said he envisions states supporting one another with troops, aircraft and other equipment. "In any state where we may be short assets to respond to a homeland mission, whether it's a tornado in a town or a fire, we can cross state lines with just a phone call or two," he said.

For example, he said, if Montana is short on helicopters this summer, it could borrow from Wyoming or other states. (A spokeswoman for the Wyoming National Guard said that state has eight Black Hawks, half of which are deployed to the Middle East.)

Overall, Grass said that he isn't aware of any state commanders who have informed his office that they cannot contribute any more troops. But he said he does know that "certain types of units have been used up -- MPs, security forces, military intelligence." The answer, he said, is to convert to those skills some less-used units, such as artillery and chemical protection forces.

Guard commanders agreed that sharing is the answer, at least in the short run. "Until the aviation picture gets fixed, that's what we're going to have to do," said Texas's Marty. "We're not going to stand there and watch another state burn."

Researcher Lucy Shackelford contributed to this report.

Spec. Henry Arnold of Houma, La., holds his 11-month-old son, Hunter, before his National Guard unit was sent on active duty last month. Some state forces are stretched thin by deployments.