Washington ? The assassination of an Afghan leader threatens the fragile central government and should compel the United States to consider an active role in providing security in the country, lawmakers said Sunday.

“This was definitely a throwback to the old Afghanistan and a setback to the establishment of the new Afghanistan,” said Sen. Bob Graham, D-Fla., chairman of the Senate Intelligence Committee, on NBC’s “Meet the Press.”

Killed Saturday by gunmen in Kabul, the capital, was Abdul Qadir, appointed as one of five vice presidents during last month’s Afghan grand council.

“I fear that we may see this government and our efforts unwind here if we don’t make the appropriate investment of men and effort and resources,” said Sen. Chuck Hagel, who serves on the Senate Foreign Relations Committee.

“If we lose there, if this goes backward, this will be a huge defeat for us symbolically in that region, in the world, for our word, confidence in Americans all over the world. We cannot allow this to go down,” Hagel, R-Neb., said on NBC.

About 7,000 U.S. troops are in Afghanistan, including infantry, special operations air and ground troops, military police and intelligence analysts. They are hunting for al-Qaida fighters and weapons, and are training an Afghan army.

Turkey commands the 19-nation peacekeeping force of more than 4,500 soldiers, primarily Europeans. They have provided security in Kabul since the Taliban militia was ousted by U.S.-allied northern alliance forces late last year.

Afghan President Hamid Kazai has asked for the force to be expanded beyond Kabul, but the United States and other countries contributing troops favor limiting its role until they can hand over responsibilities to an Afghan army.

“If all you do is secure the capital and allow instability to fester around the country, I think we’re running a real risk that the gains we made during the war could be lost by an insufficient peace,” added Sen. Evan Bayh, D-Ind.

While wanting to hear from President Bush on this issue, Bayh said on “Fox News Sunday” that “my own view is, we went to war, we won the war, let’s not lose it now. And I think we need to take stronger security steps.”

The assassination, Hagel said, shows “how fragile this situation is, and how a long-term, sustained, strong leadership position America is going to have to have if we are to win. When I say “win,” I mean just stabilize that area.”

Hagel said he thinks the United States should “take another look at … more involvement” in the international peacekeeping force in Afghanistan.

Graham said Qadir’s killing “may indicate that we are going to have to be more of a participant in some of the security activities that are necessary in order to create a climate in which the new government can be established.”

He said the shooting was “a source of considerable concern.”

Senate Majority Leader Tom Daschle, D-S.D., said on CBS’ “Face the Nation” that the slaying “illustrates the degree of challenge we still have in Afghanistan. We have a long way to go to accomplish our goals.”

Bush, vacationing over the weekend in Maine, said Saturday that Qadir’s death strengthened U.S. determination to help Afghanistan recover from war.

“We are more resolved than ever to bring stability to the country so that the Afghan people can have peace and hope,” Bush said.

Graham said the U.S. military has performed well in Afghanistan and in other recent international missions. “Where we haven’t had equal success is following up with those forces that could provide essential law and order and begin the process of restoring the basic institutions upon which any society depends,” he said.

He said the United States must “spend more effort figuring out how to do the final chapters of our involvement in nations and do them as well as we do the first.”