WASHINGTON - The Army needs to add at least 30,000 active-duty soldiers to its ranks to fulfill its responsibilities around the world without becoming stretched dangerously thin, senior Army officials warn.

"You can't do what we've been tasked to do with the number of people we have," Undersecretary of the Army Nelson Ford said in an interview last week. "You can see a point where it's going to be very difficult to cope."

Already, the Army lacks a strategic reserve of brigades trained and ready for major combat, officials said, and units being deployed to Iraq and Afghanistan are receiving new soldiers at the last minute, meaning they lack sufficient time to train together before crossing into the war zone.

But the demand for soldiers extends beyond those countries, with the Pentagon creating new missions that require troops trained in cyber-warfare, homeland defense, intelligence-gathering and other areas, Ford said.

"We have five to 10 new missions, and we are already stretched now," he said.

The Army is on track to grow to 547,000 active-duty soldiers next year, up from 482,000 before the Iraq war. But Ford and other Army officials say that, with rising demand for ground troops for Afghanistan and other contingencies, the increase is insufficient.

The service needs 580,000 soldiers "to meet current demand and get the dwell time," Ford said, referring to the amount of time soldiers have at home between deployments to train, rebuild, and spend with families.

"You can run a machine without oil for so long, and then the machine ceases," he said. "The people are the oil."

Ford's remarks come two years after Donald Rumsfeld resigned as defense secretary, removing from the Pentagon a powerful opponent to expanding the Army. Rumsfeld opposed a permanent increase in its size and instead devoted much of his tenure to turning it into a more agile force, an agenda that met with objections and dismay from senior Army officers.

The Army is also benefiting from the weakened economy, which has improved its ability to recruit and retain soldiers. Despite well-publicized recruiting problems in the early years of the Bush administration, the Army has met its recruiting goals for the last three years, and it continues to see benefits from its $1.35 billion, five-year "Army Strong" advertising campaign launched in 2006.

But President-elect Barack Obama's transition team has signaled that his administration will look to cut the Pentagon budget, of which military personnel costs are a rising share.

Planning is under way at the Pentagon to add at least 20,000 more U.S. troops to the force in Afghanistan, but the Army is facing pressure to supply not only combat brigades but also the thousands of support soldiers required to facilitate operations in Afghanistan's austere terrain.

"Logistics issues in Afghanistan are just stunning," Ford said.

And in Iraq, even as the total number of U.S. troops declines, more support forces are likely to be required, Army officials say.

"As you draw down in Iraq, you're going to need more sustainment and aviation," said Maj. Gen. Tony Cucolo, commander of the Third Infantry Division, which has been deployed to Iraq three times.

The demand for soldiers extends beyond the war zones, Ford said, as commanders in other regions request troops.

"It's a real challenge," he said.