KABUL, Afghanistan — The secretary general of NATO sought Tuesday to address fears that international forces would leave Afghanistan too soon, saying that the 43 nations in Afghanistan would stand by the country until it was ready to stand on its own.

In his remarks at a joint news conference with the Afghan president, Hamid Karzai, Anders Fogh Rasmussen, the NATO secretary general, tried to reassure those who feared that a premature withdrawal would leave the Afghan people and government vulnerable to Taliban insurgents.

“I know some are wondering how long international forces will stay; they are worried we will leave too soon,” Mr. Rasmussen said. “Let there be no doubt, the international community will stand with you and help in rebuilding your country until you are ready to stand on your own, and ensure that terrorism will never take root again.”

The NATO commitment is particularly important to the United States because it gives international legitimacy to the war. But the commitment is also important because the European members of the coalition, which includes forces from NATO and non-NATO nations, face considerable domestic opposition to having their troops in harm’s way, and at times in the past year have seemed on the brink of reducing the numbers fighting.

NATO has pledged to send 7,000 additional soldiers. President Obama plans to deploy 30,000 more American troops.

Mr. Rasmussen predicted “new momentum” in 2010, adding that the international coalition would be much larger and that it would focus more on “protecting the population, the roads and the development projects.”

Mr. Rasmussen said NATO forces would be involved in training Afghans, with the goal of transferring security responsibilities to them as soon as they are prepared. Despite Mr. Obama’s pledge that Americans will begin to come home in 18 months, Mr. Rasmussen stressed that their departure would be based on the Afghans’ ability to handle security.

“They will take the lead where and when they are ready; this transition will be conditions-based, not calendar-driven,” he said.

Asked about his recent trip to Russia to persuade its leaders to join the international effort to help Afghanistan, Mr. Rasmussen said that the Russians had yet to make any commitments, but were studying some of his suggestions, including the possibility of providing helicopters to the Afghan Army as well as training, spare parts and fuel.

In southern Afghanistan, a British soldier died Sunday during a firefight with the Taliban, according to a statement from NATO forces.

The final toll in Gardez, where the Taliban carried out an audacious attack on the local police headquarters on Monday, was three dead civilians, including one woman, and 14 wounded, several of them police officers, said Pushtun Wali, a Health Department official in the city.