WASHINGTON (CNN) -- Sen. Hillary Rodham Clinton, D-New York, will introduce a bill capping troop levels in Iraq as of January 1, and require President Bush to seek Congressional approval before sending additional troops, according to a top Senate aide.

Clinton previewed her position Wednesday on some of the morning shows. This afternoon, at a 3 p.m. news conference on her recent trip to Iraq and Afghanistan, she will formally unveil her legislation.

There may be some language about specific benchmarks required of the Iraqi government and military, and there may be co-sponsors on this bill, the aide said.

Clinton's legislation is very similar to a bill Sen. Chris Dodd, D-Connecticut, is sponsoring that would set troop levels based on January 16. Dodd is running for the Democratic presidential nomination and Clinton is widely expected to run for the White House as well.