KABUL, Afghanistan — Moving to preserve the political and ethnic balance at the top of his government, President Hamid Karzai on Tuesday nominated a prominent former Northern Alliance figure to fill the vice-presidential post left vacant by the death of Muhammad Qasim Fahim last week.

The nominee, Yunus Qanooni, is — like his predecessor — an ethnic Tajik who rose to prominence through the old Northern Alliance, which resisted the Taliban’s takeover of Afghanistan in the 1990s. Mr. Qanooni served as interior minister after the ouster of the Taliban government in 2001, and was widely seen as a political rival of Mr. Karzai.

But there was little expectation that Mr. Qanooni could fill the void left by Mr. Fahim, who was among the country’s most powerful and influential figures before he died of a heart attack on March 9. Mr. Karzai and American and European officials had been counting on Mr. Fahim to help avert a political crisis if, as many here expect, a candidate from Afghanistan’s largest ethnic group, the Pashtuns, wins next month’s presidential election.

That role — rounding up northern acceptance of the central government — would now in theory fall to Mr. Qanooni. But he lacks some of the stature commanded by the late vice president among Afghan Tajiks.