No group took responsibility for the bombs. A statement issued by the city authorities blamed ''saboteurs of foreign origin.'' It did not elaborate, but the authorities have routinely said previous bombings in Pakistan were the work of agents of the Communist Government in neighboring Afghanistan.

This was the first bombing reported in Karachi, but bomb attacks have recently become more frequent in Pakistan. Nine days ago, three blasts within a few minutes killed seven people in Lahore, Pakistan's political heartland. No Arrests So Far

No arrests have been made in the earlier attacks, and the Government of President Mohammad Zia ul-Haq has not publicly blamed any organization or country.

There has been speculation that the Lahore bombings might have been carried out by Pakistani dissidents opposed to the Government.

The explosions today were in the Saddar area, the biggest shopping district in the center of this city of more than seven million people on the Arabian Sea.