QUETTA, PAKISTAN -- Pakistan army Capt. Rana Samad and 20 men were on a routine patrol in the desert near Pakistan's border with Iran two months ago when they stumbled onto what some Western drug enforcement officials call the single largest cache of heroin ever seized.

Following a five-hour gun battle that involved hundreds of paramilitary troops and claimed several lives, Samad's men captured several mud houses in which they found more than two tons of high-quality, refined heroin worth about $500 million on the streets of Europe and New York. In addition, they seized hundreds of assault rifles, machine guns, rocket launchers, about a dozen trucks, and other equipment evidently used to move large heroin shipments by land.

In many countries, such a huge seizure would lead to promotions, press conferences and high-profile prosecutions. But that is not how the multibillion-dollar annual drug trade works in Pakistan.

Instead, the firefight and heroin seizure were kept secret for weeks; the alleged owner of the drug operation, Sakhi Dost Jan, walks freely in Quetta; and some Western drug officials worry that the captured heroin eventually will be taken from government warehouses and resold on the international market.

"The matter was taken up at the highest level in Islamabad," said a senior paramilitary officer here, adding that reports about the seizure had been forwarded to Pakistani President Ghulam Ishaq Khan and the army chief of staff, Gen. Aslam Beg. "What we knew is that we didn't get any rewards or appreciations" for the seizure, the paramilitary officer said.

To the contrary, Maj. Gen. Sardar Khalid, the chief of the Frontier Corps, which captured the heroin and guns, was transferred from his post. Military sources say his transfer was at least partially related to the heroin seizure.

Western drug enforcement specialists say the incident in Baluchistan reflects a pattern of involvement by elements of Pakistan's government in the country's booming heroin trade.

Despite occasional promises of tough action by government officials, independent drug barons, politicians, and army and intelligence service officers all continue to profit from heroin manufacturing and smuggling in this sparsely populated desert province and in the tribal belt of the country's Northwest Frontier province, these specialists say.

"They've not done anything at all to counter the power of these guys," said a Western drug enforcement specialist, referring to heroin traffickers who import poppies from mujaheddin guerrillas in Afghanistan, manufacture heroin in Pakistan and then ship the product by land and sea to Europe and the United States.

The two-ton seizure in Baluchistan "is a quick drawing back of the curtain on what has been going on at the multi-ton level for a long time. Activity of this kind cannot go on without political and institutional cooperation," this Western specialist said.

Two alleged heroin traffickers whose activities have been tracked for years by the U.S. Drug Enforcement Administration, but who have not been charged with any crime, were elected to the national assembly earlier this year. Dost Jan, the principal accused in the two-ton Baluchistan heroin case, is closely connected to several prominent politicians and has not been arrested in the case, according to Pakistani law enforcement officials.

The drug issue threatens to exacerbate already strained relations between the United States and Pakistan. U.S. law requires the Bush administration to certify early next year that aid to Pakistan -- budgeted at about $560 million annually -- will help reduce drug production and smuggling. U.S. officials say such certification would be very difficult now, since law enforcement officials in Pakistan seem disinterested in moving against drug barons, and favorable weather conditions have produced a bumper opium crop, flooding the country's export channels with heroin.

The possible suspension of U.S. aid, on grounds of lax law enforcement, may be irrelevant, since U.S. aid already has been suspended indefinitely because of concerns about Pakistan's nuclear program.