WASHINGTON -- In more than a decade of war in Afghanistan, the United States military has failed to defeat the insurgents' main weapon -- the IED, or roadside bomb -- and has been unable to prevent the spread of a deadly new Taliban tactic, the so-called "insider" attacks by Afghan soldiers on U.S. and allied troops.

Despite a strenuous and costly U.S. effort, the Taliban managed last year to deploy 16,000 IEDs, the main killer of Americans, and are on track to exceed that record this year.

Anti-western Afghans who managed to infiltrate the Afghan security forces have killed more than 50 American and allied troops so far this year, causing a significant disruption in the U.S. strategy of mounting joint operations with Afghan security forces to accelerate their combat readiness.

The twin American warfighting failures don't yet amount to military defeat, senior U.S. commanders and analysts contend. But at minimum, the explosions of IEDs and the "insider'' violence will continue to kill and maim U.S. combat troops who are scheduled to remain fighting in Afghanistan for at least two more years.

"This is a war and we will continue to fight it and fight it aggressively," Pentagon spokesman George Little said Tuesday.

He acknowledged that the insider and IED attacks have not been eliminated "entirely." But he insisted that "we have made substantial progress in Afghanistan," citing a decline in violence levels and the growth of the Afghan security forces. Attacks initiated by the Taliban are 5 percent below last year's level, according to data provided by the U.S.-led International Security Assistance Force (ISAF) command in Kabul.

"I'm not dismissing the impact of insider attacks or IEDs," Little said at a Pentagon briefing. "But to judge the progress of the war by one or two simple measures I don't think paints a true picture of the remarkable progress our men and women in uniform have made over these past 10 years."

The United States is not losing the war "in the classic military sense," Anthony Cordesman, a senior military analyst at the Center for Strategic and International Studies writes in a new analysis of American combat troops, the allies and Afghan security forces still win virtually every conventional military engagement, Cordesman writes. But he warns: "As was the case in Vietnam, the U.S. can win every battle and still lose the war."

Grim assessments by senior U.S. military officers about increasing "insider" attacks and growing IED attacks, come at a delicate moment for the Obama administration. The White House is awaiting a recommendation from Gen. John Allen, the top U.S. and allied commander in Afghanistan, on how many combat troops he believes will be needed in Afghanistan for the next two years. At present, 68,000 American troops are in Afghanistan.

With American public opinion having turned decisively against the war, Obama has promised to "end" the U.S. combat role in Afghanistan by December 2014, although the U.S. has pledged to continue some undefined military and economic support well beyond that date.

Senior U.S. officials and outside analysts agree there is little likelihood of negotiations with the Taliban that would bring a political settlement to the war.

That leaves the Obama administration with little choice but to press ahead in training Afghan security forces to take over as quickly as possible, allowing American troops to come home. But that effort has been badly hampered by the insider attacks.

Allen on "60 Minutes" Sunday acknowledged that the insider attacks, which have killed 53 U.S. and allied troops in Afghanistan this year, are a successful Taliban tactic and that the attacks will continue.

"The enemy recognizes this is a vulnerability," he said, referring to the U.S. strategy of partnering closely with Afghan forces on combat operations. Allen said the insider attacks will be the "signature" attacks of the war, along with IED strikes.

Until recently, 90 percent of military operations in Afghanistan were done with U.S. and Afghan security forces working jointly. But because of the sudden increase this summer and fall of attacks on U.S. personnel by fighters in Afghan security forces uniforms, these joint operations had been halted. But now many of the joint patrols have been allowed to resume, Little said.

That's a dangerous step, some analysts say, considering that the attacks are a deliberate Taliban tactic rather than the "cultural friction" cited by some U.S. and Afghan officials. The resumption of joint operations, said John McCreary, a retired warning officer for the CIA and the Defense Intelligence Agency, "is the ultimate proof" that commanders in Afghanistan "misunderstand the gravity and the nature of the threat. Better behavior by western soldiers will not stop the murders," McCreary writes in his blog, NightWatch.

Currently, U.S. troops rely for protection on one or more "guardian angels," a member of the unit with a round chambered in his weapon, constantly watching the Afghans in the area with whom they are assigned to work. At Forward Operating Base Shank in Logar Province, one soldier acting as a guardian angel watching an Afghan contractor explained to a Time magazine reporter, "if he starts acting up, I'm supposed to drop him."

Such tense relations inevitably damage what was supposed to be a close working relationship between Afghan and allied troops. "There's no doubt insider attacks have undermined trust and confidence, absolutely," Anders Fogh Rasmussen, the secretary general of NATO, which has provided troops from 17 nations, said this week in an interview with the Guardian newspaper.

IEDs, which have killed more than 600 American troops since 2001 and wounded roughly 7,000, will continue to be a major threat in Afghanistan "because they are cheap, readily available, largely off-the-shelf, easy to construct, lethal and accurate," Army Lt. Gen. Michael D. Barbero told a congressional panel In September. Barbero is director of the Joint IED Defeat Organization, the Pentagon agency charged with countering the IED threat. JIEDDO is budgeted at $2.4 billion this year.

Over the past two years, Barbero said, the number of IEDs deployed by the insurgents jumped 42 percent, from 9,300 in 2009 to 16,000 last year. This past June, JIEDDO recorded the highest number of IEDs in the war.

Almost all of the IEDs are made with homemade explosives fabricated from ammonium nitrate, a common fertilizer trucked over the border from Pakistan. U.S. and allied troops were unable to halt such imports even before U.S. troop strength was cut back this year from nearly 100,000 to 68,000.

In a further reminder that the Taliban remain a potent threat, 15 insurgents three weeks ago attacked Camp Bastion, a major U.S. and coalition facility in southern Afghanistan. The attackers, dressed in U.S. Army uniforms, forced their way onto the base and among other damage, destroyed six AV-8b Harrier jet strike fighters. The attackers "appeared to be well equipped, trained and rehearsed," ISAF acknowledged.

Fourteen of the attackers were killed and one was captured. But as Cordesman points out in his analysis, "the problem is that this is a political war where the political impact of combat, politics, governance and economics are far more important than tactical success in directly defeating the enemy.

"The insurgents still seem to have significant momentum and are certainly not being decisively defeated," Cordesman writes.

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  • Afghan boy walks his dog on a hill above Kabul, Afghanistan, Monday, Oct. 1, 2012. (AP Photo/Ahmad Jamshid)

  • Afghan girls ride donkeys carrying firewood for their home in the Gushta district of Nangarhar province, east of Kabul, Afghanistan, Monday, Oct. 01, 2012. (AP Photo/Rahmat Gul)

  • An Afghan girl carries firewood for her home in Gushta district of Nangarhar province, east of Kabul, Afghanistan, Monday, Oct. 1, 2012. (AP Photo/Rahmat Gul)

  • Afghan Defense Minister Besmillah Khan Mohammadi, right, and Afghan Interior Minister Mujtaba Patang, pray during a gathering in Gushta district of Jalalabad, east of Kabul, Afghanistan, Monday, Oct, 1, 2012. (AP Photo/Rahmat Gul)

  • An Afghan soldier stands guard during a gathering in Gushta district of Jalalabad east of Kabul, Afghanistan, Monday, Oct. 1, 2012. (AP Photo/Rahmat Gul)

  • Afghan Defense Minister Besmillah Khan Mohammadi, center, and Afghan Interior Minister Mujtaba Patang, left, walk in Gushta district of Jalalabad, east of Kabul, Afghanistan, Monday, Oct, 1, 2012. (AP Photo/Rahmat Gul)