WASHINGTON  American and international investigators say that they have found the electronic blueprints for an advanced nuclear weapon on computers that belonged to the nuclear smuggling network run by Abdul Qadeer Khan, the rogue Pakistani nuclear scientist, but that they have not been able to determine whether they were sold to Iran or the smuggling ring’s other customers.

The plans appear to closely resemble a nuclear weapon that was built by Pakistan and first tested exactly a decade ago. But when confronted with the design by officials of the International Atomic Energy Agency last year, Pakistani officials insisted that Dr. Khan, who has been lobbying in recent months to be released from the loose house arrest that he has been under since 2004, did not have access to Pakistan’s weapons designs.

In interviews in Vienna, Islamabad and Washington over the past year, officials have said that the weapons design was far more sophisticated than the blueprints discovered in Libya in 2003, when Col. Muammar el-Qaddafi gave up his country’s nuclear weapons program. Those blueprints were for a Chinese nuclear weapon that dated to the mid-1960s, and investigators found that Libya had obtained them from the Khan network.

But the latest design found on Khan network computers in Switzerland, Bangkok and several other cities around the world is half the size and twice the power of the Chinese weapon, with far more modern electronics, the investigators say. The design is in electronic form, they said, making it easy to copy  and they have no idea how many copies of it are now in circulation.