WASHINGTON  President Bush asserted on Tuesday that he had the executive power to bypass several parts of two bills: a military authorization act and a measure giving inspectors general greater independence from White House control.

Mr. Bush signed the two measures into law. But he then issued a so-called signing statement in which he instructed the executive branch to view parts of each as unconstitutional constraints on presidential power.

In the authorization bill, Mr. Bush challenged four sections. One forbid the money from being used “to exercise United States control of the oil resources of Iraq”; another required negotiations for an agreement by which Iraq would share some of the costs of the American military operations there.

The sections “purport to impose requirements that could inhibit the president’s ability to carry out his constitutional obligations,” including as commander in chief, Mr. Bush wrote.