Afghan Rebels Take Major Air Base Near Kabul : Asia: The move threatens to subvert a U.N. peace plan in last stage of negotiations to end the 13-year conflict.

Islamic rebels tightened their stranglehold on the territory of Afghanistan’s embattled President Najibullah on Wednesday, taking control of the major air base that protects his regime. The move threatened to subvert a hard-won U.N. peace plan for Afghanistan in the 11th hour of negotiations.

Afghan officials in Kabul, the capital, and in the regime’s diplomatic mission in New Delhi confirmed that Bagram Air Base, the Soviet-built military stronghold that has reinforced the rule of successive Afghan strongmen, was no longer in the hands of Najibullah’s forces.

All loyalist military forces in the capital were immediately placed on highest alert. It was unclear exactly which rebel faction controlled the base, since the two strongest and most fundamentalist of the moujahedeen guerrilla forces each claimed it. At the same time, the base’s former commanders, apparently still on the scene, were professing neutrality.

Rumors spread through the tense Afghan capital that Najibullah had fled to New Delhi. Ahmed Sarwar, the Afghan ambassador to India and the president’s brother-in-law, publicly denied that report, but he confirmed that the president’s wife and three daughters had been evacuated here earlier.

Stressing the magnitude of the day’s events, the ambassador added in an interview Wednesday night, “We have passed the phase of tragedy and entered the new era of disaster.”

The rebels move on the air base and two nearby strategic towns just 40 miles north of Kabul marked their most successful operation since the beginning of their 13-year Muslim holy war, an insurgency that began when the Soviet army invaded and occupied Afghanistan in late 1979. The United States backed the guerrillas with arms and money against Kabul and its Soviet supporters until Moscow and Washington agreed to stop sending military supplies to the Afghans as of the end of last year.

The “neutralization” of the base appeared to be more a diplomatic victory for the rebels than a military one. Most analysts and diplomats surmised that the base had not actually been captured but that commanders, after a brief skirmish and lengthy negotiations with at least one of the moujahedeen groups, had decided that it was wise to declare their neutrality.

Hard-liner moujahedeen leader Gulbuddin Hekmatyar, who proclaimed control over Bagram in the name of his Hizb-i-Islami, or Party of Islam, took the occasion to call for the surrender of government troops in Kabul.

“We have already requested the Defense Ministry in Kabul to order the surrender of their forces, or the moujahedeen will enter Kabul,” one of Hekmatyar’s spokesmen warned from the Pakistani border town of Peshawar, which has served as the rebel staging ground throughout the war.

Similarly, the Jamiat-i-Islami, or Islamic Movement, said that troops loyal to its charismatic and powerful commander, Ahmed Shah Masoud, held the base. But a party spokesman stopped short of saying the base would be used as a springboard to attack Kabul.

Most moderate rebel leaders and Western diplomats in Islamabad and Kabul viewed the move on Bagram as an attempt by rebel hard-liners to protect their power in any future interim government.

Benon Sevan, the personal envoy of U.N. Secretary General Boutros Boutros-Ghali, took a similarly positive view of the takeover of Bagram. After meeting Pakistani officials who were once in the vanguard of the moujahedeen campaign to create an Islamic state in Afghanistan, Sevan told reporters in Islamabad, “There is no setback to our efforts.”

Several members of rebel leader Masoud’s party agreed. “I don’t think anyone should see this as a threat to the peace process,” Masood Khalili, a supporter of the popular rebel commander, told the Associated Press in Peshawar on Wednesday. “This is more like a backup to the political process, to make sure Najib leaves like he’s promised and to make sure the U.N. comes up with a pre-transitional arrangement.”

Late last month, President Najibullah publicly declared for the first time that he will step down and yield all executive powers to an impartial 15-member interim ruling council, one that Boutros-Ghali promised last week to name “as soon as possible.”

Sources close to the president said he is prepared to leave Kabul at the end of the month, but they added that each day the United Nations delays will fuel Najibullah’s fears of an internal military coup or an all-out rebel assault on the capital.

Most diplomatic analysts in Kabul and Islamabad expressed the belief that since his public pledge to resign, Najibullah’s regime has grown more fragile by the day. They warn that Afghanistan could fall into chaos, with unrestrained bloodletting along ethnic, linguistic and religious lines, if there is no final settlement before the end of the month.

Already, dozens of heavily armed militias that fought alongside government troops both before and after the Soviets ended their occupation in 1989 have turned against Najibullah in recent months, largely for ethnic reasons.

The militias that control the country’s northern border with the former Soviet Central Asian Republics, for example, are largely minority Tajiks and Uzbeks. The president is a member of the majority Pushtun community, and he narrowly averted a move against him by the minority militia commanders last month by agreeing to cede all military power to them in the northern third of the country.

Deepening the crisis Wednesday, the rebel takeover gave the moujahedeen effective control of the strategic Salang Highway that carries food and fuel supplies from the former Soviet republics to Kabul. Food and fuel are already in short supply in the capital, and aid workers there are increasingly concerned that any additional disruption could lead to starvation.

“The real question now is, with the grain silos empty and territory falling from regime hands by the day, what happens if there’s a power vacuum in the capital?” asked one source close to the U.N. negotiations. “Who will step in and stop the blood from flowing through every street of Kabul?”