The leader of Bosnia's Serbs is beginning to make good on his promises to Jimmy Carter, and the former

president could be on his way to Bosnia this weekend to try to arrange a cease-fire, a senior Clinton administration official said Thursday.Carter would go without the specific approval of Clinton, who talked to Carter last week before the former president received an emissary from Bosnian Serb leader Radovan Karadzic in Atlanta and again Wednesday afternoon.

"He didn't say `go,' he didn't say `don't go,' " the senior official told the Associated Press. "President Carter asked for information on whether the assurances were being kept and then will make his own judgment."

Karadzic, through the emissary, had promised Carter the Serbs would observe a cease-fire around Sarajevo, the Bosnian capital, and let U.N. humanitarian convoys operate freely.

The Serbs seem to be implementing their assurances, said the official, who spoke on condition of anonymity. "President Carter could be on his way in 24 hours," the official said.

Meanwhile, Dee Dee Myers, the White House press secretary, said she did not know whether Carter had made a firm commitment to go to Bosnia.

She said if Carter went it would be as a private citizen, not as a presidential emissary.

For the third time this year, the former president has waded into a foreign policy matter confounding the White House. With cautious approval from Clinton, Carter defused a nuclear standoff in North Korea and headed off a U.S. invasion in Haiti.

Defense Secretary William Perry expressed his doubts Thursday at a NATO meeting in Brussels, Belgium, citing Karadzic's cease-fire offer to Carter.

"To the extent that Karadzic follows through on that proposal, that will be a positive step. Past history of offers from Bosnian Serbs have indicated there's some need for scepticism," Perry told reporters.

NATO Secretary-General Willy Claes was more blunt. "I do not see why it is necessary to ask the former president of the United States to come in in order to obtain simply a cease-fire, because there is no more than that in the paper of Karadzic."

"President Carter indicated that if he goes to Bosnia, he would do so as a representative of the Carter Center and that he would do so only if there were clear evidence that the commitments outlined by (the Serbs) were being fulfilled," Myers said Wednesday night in a statement that subtly distanced Carter from the White House.

The statement was issued only after Carter announced that he met representatives of Karadzic at his Plains, Ga., home and secured promises that would return U.N. operations in Bosnia to the shaky status experienced before an escalation of tensions last month.

The Bosnian Serb leader told CNN he would allow the free movement of U.N. convoys, release all U.N. personnel whose movement has been restricted and release all Muslim prisoners of war under age 19.

He also said he would order a unilateral cease-fire in and around Sarajevo, reopen the Sarajevo airport for humanitarian flights and guarantee human rights.

But on Thursday ground fire hit a helicopter in Bosnia that had been sent for the commander of U.N. peacekeepers, whose mission has appeared increasingly untenable in recent weeks.

The helicopter was forced to land, U.N. officials said. Lt. Gen. Sir Michael Rose, the U.N. commander for Bosnia, was not aboard and there were no reports of injuries.

There were contradictory reports about whether the helicopter was shot at over Bosnian Serb- or government-held territory. But it emphasized the U.N. forces' vulnerability in the war.

By reaching out to Carter, the Serbs hope to keep U.N. peacekeepers in Bosnia. If the United Nations left, the Bosnian Army could be rearmed against the Serbs. And Karadzic is aware that U.N. forces have cemented Serb territorial gains in nearby Croatia.

Myers said the development does not change U.S. policy.