OSHKOSH, Wisc. - U.S. Defense Secretary Robert Gates said on Thursday the U.S. troop presence in Afghanistan, currently under presidential review, was not open-ended, putting more pressure on Kabul to improve security and fight corruption.

President Barack Obama, in the final stages of a review expected to add tens of thousands more U.S. troops to the stalled campaign, asked his national security team on Wednesday to set a timetable for the Afghan armed forces to assume greater security responsibility, officials said.

Gates, speaking to reporters on a flight to Oshkosh, Wisconsin, said Obama wanted through his decision on troop levels to signal resolve and at the same time, signal to the Afghans as well as to the American people that this isn't an open-ended commitment.

He said he was appalled by media leaks that have accompanied the decision process. In the latest on Wednesday, officials disclosed that U.S. ambassador to Kabul Karl Eikenberry had sent cables back to Washington objecting to the proposed surge of tens of thousands of US troops until Afghan President Hamid Karzai demonstrated he was willing to tackle endemic corruption and mismanagement.

Karzai's credibility that badly damaged after he won an election marred by rampant vote rigging. But Washington has no other partner in Afghanistan.

Obama's strategy review has involved, among other things, how to combine some of the best features of various options presented to him by his advisors, Gates said.

Key advisers including Gates and top military commanders favor sending at least 30,000 more U.S. troops as part of an expanded counter-insurgency plan, U.S. officials have said.

Skeptics led by Vice President Joe Biden, question whether a troop increase will work given doubts about Karzai's legitimacy and his willingness to fight corruption.

The leak of Eikenberry's cables revealed a serious rift within the administration.

In Wisconsin, Gates toured a plant building a new class of trucks designed to withstand roadside bombs and cope with Afghanistan's rugged mountain terrain.

He said he was setting up a task force to boost U.S. offensive and defensive efforts against roadside bombs, which the military calls improvised explosive devices, or IEDs.

Gates said if Obama decided to send more troops, they might be buying more of the all terrain vehicles made by Oshkosh Corp, a Wisconsin truck maker.

More than 80 percent of U.S. casualties in Afghanistan were being caused by IEDs, Gates said.

(Editing by Alan Elsner)