ASHINGTON, Sept. 29 ・The United States has now amassed a military force of 28,000 troops, more than 300 warplanes and two dozen warships in the region surrounding Iraq and Afghanistan, enough firepower to allow President Bush to strike at any moment should he so decide.

The diverse forces, stretching from the Indian Ocean to the Red Sea, bring a potent range of military options with them to keep pressure on those two isolated nations. But senior Pentagon officials acknowledge that those options are in many ways both imperfect and risky.

Although President Bush and his defense secretary, Donald H. Rumsfeld, say the campaign against terror will be a new kind of war, the force in the region still relies predominantly on air power, with all its limitations, the officials said. Conventional wars are ultimately won by taking and holding territory, as one military maxim has it, but that is not an option being considered now.

The Pentagon has also mobilized special operations troops ・their numbers are secret ・but they are now playing mainly a supporting role to possible air and missile strikes, the officials said.

For now, other ground forces are most likely to play mainly protective roles in places like Kuwait.

The United States has recently dispatched B-52 and B-1 bombers to the region and has Navy F-14's and F-18's aboard nearby aircraft carriers. Air Force F-15's routinely enforce no-flight zones over Iraq, where American and British warplanes have continued to skirmish with Iraqi air defense forces even since the Sept. 11 terrorists attacks.

So far, the Bush administration has resisted temptation to retaliate immediately for the attacks on the World Trade Center and the Pentagon as it rallies broader international support for battling terrorism and gleans intelligence on the whereabouts of Osama bin Laden and his allies.

The question of how to battle terrorists in their remote and rocky Afghan havens has perplexed military planners in both the Clinton and Bush administrations, some of whom share a darkly comic answer when asked about the war plan.

"It's called A.O.S.," they say, using a barracks retort for "all options stink." Another senior military official said there was "no good option that wouldn't make us look useless."

Even a series of precisely calibrated strikes would require a vast and expensive network of bases, command posts, flight decks, refueling outposts and defensive weapons, with all the accompanying logistics.

A senior Air Force officer said late this week that the Bush administration was still negotiating for all the support for overflights and for basing aircraft it would like in the region.

John Bolton, the under secretary of state, ended the week in talks with Central Asian countries that border Afghanistan.

A senior official said that negotiations this week in Pakistan had given the United States significant access to bases there, mainly for search and rescue operations and reconnaissance.

"Some people were actually pleasantly surprised how much they agreed to," a Pentagon official said.

Ever since the Persian Gulf war in 1991, the United States has maintained a significant military presence in the region, largely to keep President Saddam Hussein of Iraq in check.

At any given time, those forces number more than 20,000 troops, nearly 200 fighter and support aircraft and at least one aircraft carrier and its accompanying warships, which include submarines, cruisers and destroyers able to fire scores of long-range cruise missiles.

Since the terrorist attacks, President Bush has greatly bolstered that force.

Immediately after the attack, he ordered the aircraft carrier Enterprise and its battle group to remain in the region after the carrier Carl Vinson arrived in the Persian Gulf, instantly doubling the naval firepower normally stationed there.

Each carrier has roughly 75 aircraft ・half of which are F-14's and F-18's attack jets ・capable of conducting around-the-clock airstrikes for days at a time.

Two other carriers ・the Theodore Roosevelt, headed to the Mediterranean Sea, and the Kitty Hawk, which recently steamed out of its home port in Japan ・could also join the operation, but have not yet received orders to do so, officials said.

President Bush also ordered the Air Force to send nearly 50 combat aircraft to the region, including B-52 and B-1 bombers now on Diego Garcia, the British island in the Indian Ocean, according to officials familiar with the preparations.

Although Diego Garcia is thousands of miles from Afghanistan, the bombers have more than enough range to reach their targets.

The B-52's, Vietnam-era bombers in most cases older than the pilots flying them, are equipped with 20 cruise missiles able to travel as far as 1,500 miles to their targets. The B- 1's, which as recently as NATO's air war against Serbia in 1999 were relegated to what the Air Force no longer likes to call "carpet bombing," now carry up to 24 satellite-guided 2,000- pound bombs.

The Air Force has also dispatched an armada of aerial refuelers, reconnaissance aircraft and other support aircraft to bases in Turkey, Kuwait, Oman and Saudi Arabia, bringing the total of American aircraft in the region to more than 300, the officials said.

All told, roughly 6,000 additional American troops have poured into the region since the attacks. Those new troops include additional security forces as well as Army Special Forces units.

The United States has relatively few ground forces in the region. When the terrorist attacks occurred, the Army had about 3,000 troops there, mostly in Kuwait, Qatar and Saudi Arabia. The largest group is a heavy task force in Kuwait, with about 1,100 troops, that has been there for a decade in case Saddam Hussein decides once again to attack Kuwait.

The Army also maintains a stockpile of equipment in Kuwait, along with two Patriot air defense batteries. Another Patriot battery is in Saudi Arabia.

A brigade's worth of equipment has been positioned in Qatar and another brigade's worth is afloat in the region.

Britain also has a significant force in the region, including more than 20,000 troops, an aircraft carrier, several other warships and dozens of aircraft, all taking part in a previously scheduled training exercise with Omani forces.

The force, Britain's largest single military deployment since the Falklands war in 1982, could easily switch from its training to take part in an American-led operation, officials in Washington said.