A crooked accounting whiz pleaded guilty yesterday to helping create $1 billion worth of phony tax shelters for big-bucks clients of the BDO Seidman firm.

Charles Bee Jr., 63, faces 15 years in prison, but prosecutors promised to seek leniency if he cooperates in the probe of the massive fraud, which allowed clients to evade more than $200 million in taxes.

The former partner of the accounting company agreed to forfeit $20 million in ill-gotten gains, including three homes in Boca