Public opinion is turning against U.S. involvement in Libya.

According to a newly released Gallup Poll, 46% of respondents disapprove of the Libyan military action, while 39% approve. Fifteen percent have no opinion.

This is a near-reversal of public opinion since March, shortly after the Libya mission began. Back then, 47% approved, while 37% disapproved and 16% had no opinion.

The new poll comes as the U.S. House plans to vote today on two resolutions, one that would grant limited authority to the Libya mission -- and another that would cut off funds for the operation.

Most of the critics oppose the conflict on principle, as opposed to the recent political dispute over whether President Obama should have obtained congressional authorization for U.S. participation.

Among the critics, 64% said the United States should not be involved in Libya at all. Twenty-nine percent oppose the conflict because Obama did not seek congressional approval.

Some members of Congress say the Libya effort violates the 1973 War Powers Resolution, which requires presidents to seek congressional authorization within 90 days of military action.

President Obama's legal team says Libya is not subject to the War Powers Resolution because the United States plays a support role in an operation led by NATO.

Among the poll respondents who back the Libya mission, 85% say it should continue until dictator Moammar Gadhafi is removed from power.

There's a bit of a gender gap in support of the war; 47% of men back U.S. involvement, while 32% of women do so.

Among the groups that support the military action: Democrats (54%), liberals (50%), and post-graduate students (51%).

Gallup's analysis:

Gallup found initial support for the U.S. mission in Libya low compared with other recent U.S. military engagements.

As the operation continues into its fourth month, and with increased criticism of the effort from political leaders, it is not surprising that support for it has eroded. It is still unclear whether Congress will ultimately limit the mission in Libya or authorize it to continue.

The president's Wednesday announcement of troop withdrawals from Afghanistan shows he is sensitive to pressure to scale down U.S. military operations abroad as the U.S. struggles to improve the economy and get the federal budget deficit under control.

See photos of: Barack Obama, Libya, Moammar Gadhafi