TOKYO — International donors will pledge $16 billion in aid for Afghanistan over the next four years in hopes of stabilizing the country after most foreign combat troops return home, a U.S. diplomat said Sunday, but the money will come with conditions to ensure it doesn’t fall victim to rampant Afghan corruption and mismanagement.

The announcement was expected today at a Tokyo conference attended by about 70 countries and organizations. The American official travelling with U.S. Secretary of State Hillary Rodham Clinton spoke ahead of the event on condition of anonymity and said $4 billion per year would be promised from 2012 through 2015.

The U.S. portion is expected to be in the decade-long annual range of $1 billion to this year’s $2.3 billion. Officials declined to outline the future annual U.S. allotments going forward, but the Obama administration has requested a similarly high figure for next year as it draws down American troops and hands over greater authority to Afghan forces.

The total amount of international civilian support represents a slight trailing off from the current annual level of about $5 billion, a number somewhat inflated by U.S. efforts to effect a “civilian surge” for Afghan reconstruction, mirroring President Barack Obama’s decision in 2009 to ramp up military manpower in the hopes of routing the Taliban insurgency.

Still, it is a large sum designed to allay fears that Afghanistan will be abandoned when NATO and other international soldiers leave.

The donors’ meeting in Japan is expected to establish a road map of accountability to ensure that Afghanistan does more to improve governance and finance management and to safeguard the democratic process, rule of law and human rights — especially those of women.