Pakistan appears to have suspended the controversial new program to transfer U.S.-supplied Stinger antiaircraft missiles to Afghan rebels and is also limiting the deployment of a similar weapon the United States is reported to be supplying, the British-built Blowpipe, according to sources in Pakistan and Afghanistan.

In a role it took on secretly several years ago but which has since become generally known, Pakistan is the main pipeline for funneling weapons to the Afghan resistance fighters battling the Soviet occupation of their country. Sources here and in Islamabad, the Pakistani capital, say the new limitations on the missiles are primarily due to Pakistan's own security concerns, including worries over possible Soviet retaliation.

It is not clear, these sources said, whether the suspension of the Stinger deliveries is temporary or permanent.

Aside from security concerns, there are also indications of technical problems with the Stingers.

Several sources interviewed here and inside Afghanistan during a recent reporting trip spoke of Stingers having been deployed in defense of Afghan guerrilla bases in Afghanistan at Jawar in April and Jaji in May. The sources said the missiles had repeatedly misfired. A knowledgeable western observer suggested that rough handling and continuous exposure to hot sun might have damaged the electronic heat-seeking system of the Stingers.

The mujaheddin -- as the rebels fighting the Afghan government and the Soviet troops supporting it are called -- who reported the spring deployment of Stingers, said they had now been withdrawn. One informed Pakistani military analyst, while not confirming the Stinger deployment, said Pakistan -- which controls the delivery of U.S.-supplied weapons to the mujaheddin -- is now blocking the delivery of Stingers to the Afghans.

The Stinger project "was aborted at some stage of the implementation," he said, because "introducing U.S. equipment means escalation." "Our government and military people are not ready for it," the analyst said.

"If the Soviets decide on a confrontation with us at some stage . . . we're not sure what the United States will be ready or able to do" to guarantee Pakistan's security, he said.

Accounts of the deployment of these modern weapons underline the heavy pressure that Pakistan faces as a vulnerable front-line state in what is partly a superpower confrontation in neighboring Afghanistan.

The Reagan administration is pressing Pakistan to allow stepped-up support for the Afghan resistance. But Pakistani officials appear fearful of cooperating, largely because they continue to doubt the United States' commitment and ability to help defend Pakistan in case of a serious threat from the Soviet Union.

In March, the Reagan administration, in a major shift of U.S. policy, decided to send the sophisticated shoulder-held Stingers to Afghan and Angolan rebels, informed sources said at the time.

The shift occurred after activists in the Pentagon and the CIA, backed by conservatives in the Senate and elsewhere, overcame opposition by State Department officials, and some in the CIA, it was reported.

Opponents of the shift argued that introducing U.S.-made arms into Third World conflicts would escalate those struggles into U.S.-Soviet confrontations and that there were no guarantees that such advanced weaponry would not fall into terrorist hands. But in the interagency deliberations that led to the policy change, those concerns were overcome by the argument that -- in Afghanistan's case -- the anticommunist forces were in dire need of antiaircraft missiles to defend against Soviet helicopter gunships and jets.

Although the Blowpipe is British-made, there is no evidence of a direct British role in its transfer or use in Afghanistan. All suggestions from Afghan and Pakistani sources are that the Blowpipe is being supplied by the U.S.-sponsored arms pipeline. One resistance source here said the new antiaircraft missiles were coming by "normal channels." Western diplomats in Islamabad suggested that the United States purchased the Blowpipes directly from Britain.

The Stinger is billed as highly effective and portable. Its advanced heat-seeking technology allows its operator to fire at an oncoming aircraft from more than five miles away. The Blowpipe is also a lightweight, hand-held weapon effective against low-flying aircraft. Like the Stinger, it needs no outside energy source.

In interviews over recent weeks, Afghan rebel sources and Pakistani analysts have said Stingers and Blowpipes were fired at Soviet aircraft supporting Afghan government offensives in Afghanistan's eastern Paktia province during April and May. While several accounts positively identified some of the missiles as Blowpipes, there have been no confirmed sightings of Stingers.

All the sources interviewed about the deployment of western missiles into Afghanistan spoke on condition their names not be used.

The Pakistani and Afghan sources agreed that the missiles -- fired in defense of guerrilla bases at Jawar in April and Jaji in May -- had proved largely ineffective. Pakistani and western military analysts suggested the major problem was inexperienced operators, although several sources said some missiles had technical problems.

One westerner described a videotape made by the mujaheddin that appeared to show a Blowpipe being fired and exploding just underneath a Soviet SU25 ground attack jet. "The mujaheddin have no weapon in their arsenal that will catch a jet and explode near it," the western source said. "But a Blowpipe can be fitted with a proximity fuse, which would be the logical thing if you're giving it to inexperienced people, whose aim is not very good."

Although the Afghan resistance groups publicly tell western journalists they have no news of Stingers or Blowpipes being deployed, a rebel source quoted mujaheddin commanders in Paktia as saying there was "some other kind of missile other than Stinger that exploded nearby planes but did not destroy them." A western military specialist suggested that, set to explode in proximity to aircraft, the Blowpipes have proved not powerful enough to destroy SU25s, which are armored on the underside.

Unconfirmed reports from Afghan sources here said the Pakistani military, anxious to prevent the fall of the mujaheddin bases just on the Afghan side of the border, had sent officers into Afghan territory to fire the missiles. Although Pakistan denies any role in aiding the mujaheddin, a western diplomat in Islamabad said Pakistani officers "are known to go inside" Afghanistan.

Pakistan specialists on Afghanistan based in Islamabad said the missiles at Jawar and Jaji had been fired by Afghans. "Blowpipe has been fired for testing purposes, but it hasn't been in properly trained hands yet," a Pakistan military analyst said.

Military and diplomatic analysts in Pakistan have assumed that part of Reagan's Stinger initiative called for Pakistani officers -- many of whom speak one of the two major Afghan languages -- to train mujaheddin on the missiles. Reports of such training have emerged this spring, but there has been no direct evidence of them.

One westerner who visited a resistance office in the Pakistani border town of Miramshah, near Jawar, found them holding a Blowpipe they said had proved faulty. "They were keeping it in an air-conditioned room, which means someone has probably taught them how to take care of it," he said.

The Stinger deployment is the second U.S. aid program for the Afghans to be stalled by Pakistan. Early this year, the government of Prime Minister Mohammed Khan Junejo prevented the startup of a $15 million program to send humanitarian aid to Afghans inside Afghanistan.

The Junejo government has not publicly explained the delay, although western relief workers say that Pakistani fears of raising their profile as a major source of support for the mujaheddin was the main reason.

Pakistani officials here and in Islamabad express deep concern over what they say is a clearly Soviet-inspired campaign being waged by the Afghan government to undermine Pakistan's support for the mujaheddin.

A wave of terror bombings in the sensitive Pakistani borderlands has coincided with a sharp increase in border violations by Afghan forces, and a recent Soviet warning against any Pakistani development of a nuclear weapon.

"It is all a pattern of pressure to remind the Pakistanis who carry the big stick in this region," a senior official said.

Western analysts suggested that Pakistan had permitted the limited deployment of western missiles last spring because of a combination of U.S. pressure and Pakistan's concern that the mujaheddin should maintain important parts of their supply operation on the Afghan side of the border. In particular, the fall of Jawar might have been used by Moscow and Kabul to strengthen their argument that the resistance operates entirely from Pakistan