President Reagan's determination to bolster world resistance to Soviet colonialism and to crack down on the international drug trade, two seemingly unrelated goals, have come into collision in Pakistan.

The president wants to send billions of dollars worth of military equipment to Pakistan, whose national airline allegedly is a conduit for narcotics. Indeed, the State Department apparently has known for seven years that Pakistan International Airlines is used by smugglers to transport drugs.

"Available information indicates that PIA is a major conduit for illicit narcotics from Pakistan to Western Europe, the Far East, Canada and the United States," warns one of several secret documents examined by my associates Jack Mitchell and Indy Badhwar.

The drugs "are smuggled aboard PIA planes" and are "hidden in luggage and various compartments inside the aircraft" one report states.

In the past, the CIA relates, "crew luggage [was] not marked as belonging to a specific crew member, so if the bag containing narcotics should be discovered it cannot be sourced to any one individual."

The dope traffic is no penny-ante operation, CIA documents make clear. Amounts smuggled out of Pakistan have ranged from small packets of opium to one incredible load of 1,700 kilos -- nearly two tons -- of hashish.

Pakistan has become the drug-smuggleing capital of Asia, and the Karachi airport is the center, with international flights leaving every day. As a result, "narcotics networks, organized by major international traffickers, have become increasingly active," according to one CIA report.

There are reports that suspicious-looking containers have been secreted aboard PIA planes. For example, I have learned that cartons marked as stereo equipment had been hidden above airliner galleys.

The suspicious packages were "in a critical section of the fuselage with naked wires that could have caused shorts and fires," inspectors reported. The Pakistanis had asked the airplane maker to give PIA written assurance that such irregular storage was in fact routine and permissible. But sourcs familiar with the exchange said the request was turned down by the manufacturer on grounds that the storage was a violation of safety rules.

In a meeting with State Department officials, PIA representatives said there was "little chance to incarcerate or remove from service those PIA personnel involved in drug trafficking" because, as they lamely explained, the employees have a powerful union.

How high up the smuggling extends is not documented. But several years ago a PIA security official himself was arrested in Frankfurt on charges of drug smuggling.

Maybe the generals in Pakistan's military dictatorship are unable to halt the deadly traffic in drugs; maybe they don't want to. In either case, their failure to do so is hardly a recommendation for supplying them with military aid.

Yet the Reagan administration is going ahead with the proposed aid package, which is to include some of our most sophisticated fighter planes. Apparently, the decision has been made that it is more important to cultivate an ally than to make an issue of drugs.

Critics, meanwhile, have questioned the wisdom of putting the United States on the side of yet another repressive dictatorship. Diplomatic and intelligence sources have warned that for all its apparently tight control, the military regime is in serious danger of toppling from internal pressures. Far from being a stable ally, these critics warn, President Zia may turn out to be another shah of Iran.