There are already more than 100,000 international troops in Afghanistan working with 200,000 Afghan security forces and police. It adds up to a 12-1 numerical advantage over Taliban rebels, but it hasn't led to anything close to victory.

Now, the top U.S. and NATO commander in Afghanistan is asking for tens of thousands more troops to stem the escalating insurgency, raising the question of how many more troops it would take to succeed.

The commander, Gen. Stanley McChrystal, says the extra forces are needed to implement a new strategy that focuses on protecting civilians and depriving the militants of popular support in a country where tribal militias may be Taliban today and farmers tomorrow.

The White House said Tuesday that President Barack Obama has nearly finished gathering information and advice on how to proceed in Afghanistan, where bombings killed eight more American troops. With October now the deadliest month for U.S. forces in the war, many experts question the need for more troops.

"The U.S. and its allies already have ample numbers and firepower to annihilate the Taliban, if only the Taliban would cooperate by standing still and allowing us to bomb them to smithereens," said Andrew Bacevich, a professor of international relations and history at Boston University, and one-time platoon leader in Vietnam.

"But the insurgents are conducting the war in ways that do not play to (allied) strengths."

The Taliban rebels are estimated to number no more than 25,000. Ljubomir Stojadinovic, a military analyst and guerrilla warfare expert from Serbia, said that although McChrystal's reinforcements would lift the ratio to 20-1 or more, they would prove counterproductive.

"It's impossible to regain the initiative by introducing more foreign forces, which will only breed more resentment and more recruits for the enemy," he said. "The Soviets tried the exact same thing in Afghanistan in the 1980s with disastrous results."

McChrystal's defenders say the U.S. has learned from Soviets' mistakes. At his instruction, NATO troops are increasingly abandoning heavy-handed tactics.

"In the end this (conflict) cannot be solved by military means alone, and in that sense a precise figure of Taliban fighters is not the point," said NATO spokesman James Appathurai.

The U.S. says it's already adjusting its strategy to shift the focus from hunting down and killing Taliban fighters to protecting civilians — in some cases allowing insurgent units to remain untouched if they are not deemed an imminent threat.

McChrystal has also insisted that ground commanders use airpower only as a last resort and when they are absolutely sure civilians are not at risk. As a career Special Forces officer, McChrystal is likely to use small maneuverable units rather than large, heavily armed formations.

Also, experts say guerrilla numbers are not the most important factor in a counterinsurgency campaign. Instead, the number of U.S. troops depends on more complex calculations, including the size and location of the population, and the extent of the training effort for the Afghan security forces.

Appathurai said the goals of the Afghanistan strategy are key to determining how many forces are required. The goal is to have enough troops in populated areas to protect the citizenry and to provide the forces needed to train the Afghans.

In addition, while there may be as many as 25,000 Taliban, it is not a monolithic group like an army, with a clear chain of command that has to be confronted soldier for soldier. Instead, it is a scattered and diverse mix of insurgents, some more ideologically motivated than others.

There are currently about 104,000 international troops in Afghanistan, including about 68,000 Americans. Afghan security forces consist of 94,000 troops supported by a similar number of police, bringing the total Allied force to close to 300,000 members.

The 12-1 ratio may be misleading because two-thirds of the Allied force is made up of Afghans, who lack the training and experience. The Taliban usually fight in small, cohesive units made up of friends and fellow clansmen. A more meaningful ratio, then, might be 4-1 or 5-1.

Historically in guerrilla wars, security forces have usually had at least a 3-1 advantage.

At the height of the U.S. ground involvement in South Vietnam in 1968, the 1.2 million American troops and their allies outnumbered the Communist guerrillas by about 4-1. French forces in the 1945-54 Indochina war numbered about 400,000 men, only a slight numerical advantage against the rebels.

In a more recent campaign, Russia's Chechen war in 1999-2000, Russian troops held a 4-1 advantage over the insurgents.

Publicly, NATO and U.S. officials have been tightlipped about Taliban strength, arguing the guerrillas, split into a number of semiautonomous factions, regularly slip in and out of Afghanistan from Pakistan — making numbers a matter of guesswork.

But several officers at NATO headquarters in Brussels say the alliance does have reasonably accurate estimates of the number of enemy combatants its troops are facing in Afghanistan.

"The internal figure used for planning purposes is 20,000 fighters, with several more thousand auxiliaries — mainly members of tribal militias, clans, and semi-criminal gangs," said a senior officer based at NATO headquarters in Brussels. He asked not to be identified under standing regulations.

Another senior official — a representative of a non-NATO nation based at alliance headquarters — gave a similar number.

This official added that enemy numbers varied widely over time, depending on the season and other factors. "When the poppy is good, they stay home. When the poppy is bad, they take up guns," he said, speaking on condition of anonymity because of the sensitivity of the matter.

Recent U.S. government estimates have also put the number of Taliban fighters in Afghanistan at about 25,000.

Sometimes remaining small gives guerrillas certain advantages. British forces in Northern Ireland found it relatively easy to monitor and penetrate the Irish Republican Army when its ranks were swollen in the 1970s, but had a tougher time once the IRA slashed staff and regrouped into secretive four-person units.

Some analysts suggest that a NATO force much larger than the one under consideration would be needed to subdue the Taliban.

"The ratio of friendly to enemy forces would be a crucial aspect only if you could actually get at the enemy. But with an enemy that doesn't wear uniforms and hides among the population, that's very hard to do," said retired Army Col. Peter Mansoor, who helped oversee the "surge" of U.S. forces into Iraq in 2007-2008.

"The crucial aspect in this case is the ratio of security force to population — this is much more relevant," he said. "This would require one security person to every 50 people. In a country of about 32 million, this means about 600,000 security personnel would be needed to clamp it down."