Afghan violence spilling over into neighboring Pakistan?

On a recent hot and sultry evening a powerful explosion heard six miles away destroyed a two-story residential building on the outskirts of this colorful and high-spirited pushtun frontier town.

The bombing attack, apparently directed against Afghanistan guerrillas, signals a new development in the Afghan rebel-Soviet conflict: a spillover of the fighting into neighboring Pakistan.

The explosion puts Pakistan in an extremely sensitive position. It has attempted to stay out of the conflict, insisting all along that it has done nothing to back rebel activity against Moscow.

Pakistan government authorities, who rapidly ordered armed police to cordon off the area and prevent foreign reporters from visiting the scene, say at least 11 persons were killed and four seriously injured. They contend it is still too early to determine the cause. So far, no one has claimed responsibility for the bomb attack. But suspicion immediately falls on Afghan communist infiltrators and rival political resistance groups.

The Peshawar bomb attack is not the first affecting Afghan exile resistance. But it is definitely the most serious.

The government-muzzled Pakistani press briefly reported the incident, but neglected to point out that the destroyed house was rented by the Jamiat-e Islam , one of the six major Afghan rebel groups who have sought refuge across the border here.

It also failed to note that the casualties were mainly Afghan mujahideen (freedom fighters). Reliable sources here maintain it was common knowledge that the building served as the political faction's military headquarters.

Pakistani President Zia ul-Haq is nervously conscious of Soviet accusations that his country is harboring armed Afghan guerrillas.

So he is reluctant to encourage any unneccessary publicity that suggests military activity among the estimated 800,000 Afghan refugees who have flocked across the border over the past two years. With the heightened fighting between the Soviets and the mujahideen along Afghanistan's frontier provinces, the government is further determined to publically insure the Afghans stick to their refugee status. This has not prevented Islamabad from putting up with Afghan political operations on its own soil.

Early last month, two artisan gunshops in the Pakistani tribal town of Darra near the Afghan frontier were mysteriously blown up on consecutive nights.

It is no secret that many mujahideen secure their arms and ammunitions - and sell captured Soviet weapons -- in the Darra gun bazaar.

And it is in Darra, where Pushtun artisans faithfully reproduce arms ranging from the highly popular AK-47 Kalashnikov automatic rifles to the more traditional World War I Enfield .303s in family workshops.

Resistance groups in Peshawar are conspicuously aware of communist infiltrators. But they are just as uneasy about possible sabotage or espionage attempts by rival re sistance groups.

The rebel groups post armed guards in the doorways of their headquarters, set up in rented buildings in the bazaars or in the more spacious Peshawar suburban villas.

Outsiders are carefully frisked. Knives, guns, and pieces of rope are confiscated and placed in piles next to the entrances to be retrieved when leaving.

"We know very well that the communists have infiltrated their people in our group," said a former Kabul engineering student of the Jamiat-e Islam. "We have to be very careful. They try to find out who we are and whether we still have relatives bck in Afghanistan. Our friends and family will then be arrested and killed."

Resistance members usually refuse to divulge their names for fear of endangering their families.

The Pakistanis haven't apparently dismissed the possibility of communists from Kabul being responsible for the Peshawar bomb attack. But they recently called an extraordinary meeting with mujahideen representatives.

Sources indicate the secret conference was aimed not only at establishing whether any of the groups -- five of which have joined in a shaky alliance -- were responsible, but also to warn the insurgents not to carry their heated rivalries onto Pakistani soil.

"As far as I am concerned, they are nothing but refugees," says a senior government official. "But if they start introducing bloodshed into the bazaar, then let me assure you, we will crack down hard."

Security precautions in the Northwest Frontier Province have already tightened since the Darra attacks. The provincial home secretary in Peshawar revealed Pakistani police are searching for guns and explosives.

Jamiat-e Islam, an alliance member, and Hizb-e Islam, which has remained outside, are notoriously bitter enemies. Several serious shootouts have been reported in recent months between supporters of the two factions inside Afghanistan.

These have come despite Hizb-e Islam assurances that, although the rebels may be divided politically, they have enough troubles with the Soviets.