Prodded by national security adviser Frank Carlucci and congressional allies, President Reagan is considering this dramatic riposte to critics of his Persian Gulf policy: The War Powers Act is unconstitutional and cannot be used to limit presidential initiatives there or elsewhere.

In a mood reminiscent of Reagan's famous ''make my day'' crack at would-be tax hikes, the White House and its Senate allies seem to be spoiling for a political battle over the 1973 act. They are backed by legal specialists in the State Department and some esteemed Democrats, including Eugene Rostow, now a Pentagon consultant.

This White House mood, hinting at a possible out-of-the-trenches offensive, could mean modest political resurgence in this twilight period. It is reinforced by unexpected success in the Senate, where GOP leaders succeeded in blocking a vote on the defense authorization bill, which would shred Reagan's freedom of action. The strategy of Senate Republican leader Robert Dole is to protect presidential power over the ABM treaty and nuclear weapons testing.

Up to now, the White House has simply refused to agree that the War Powers Act applies to the Persian Gulf crisis. The law's requirement for consultation with Congress over re-flagging Kuwaiti tankers has been gently bypassed. Consultation there has been, but not under conditions set by the act.

To correct this, Senate Foreign Relations Committee Chairman Claiborne Pell is pushing a resolution that requires Reagan to admit the relevance of the War Powers act and to comply fully with all its terms in the Persian Gulf initiative.

State Department legal adviser Abraham Sofaer has quietly counseled Secretary of State George Shultz to let Majority Leader Robert Byrd bring Pell's resolution to the floor for a vote in a constitutionality test. Even if it passed (which is highly doubtful), the president's veto could not conceivably be overridden. Rostow, undersecretary of state in the Johnson administration and former dean of the Yale Law School, and Sofaer say privately the Senate would have trouble finding a court to take the case.

The president's men are trying to get out of the trenches and, making a virtue of Reagan's foreign policy trouble with the Democratic-controlled Congress, go on the attack. It would aim at transforming a policy of fear over getting trounced by Congress on Persian Gulf policy into a policy of confidence that the Constitution is Reagan's solid ally in giving him the policy-making power. Rank-and-file voters would be with the president.

Dole's success on the defense bill is mortar for this strategy. The quite unexpected defeat of Democratic efforts to bring up the bill was conceded over the weekend when Senate Armed Services Chairman Sam Nunn privately notified Sen. John Warner, the committee's ranking Republican, that the filibuster had worked.

Giving up his fight to invoke cloture, Nunn told Warner he was planning to head down a highly unusual road. Democratic staffers of Nunn's Armed Services Committee would begin to write a final Pentagon spending bill in negotiations with staffers of the Senate Appropriations Committee, completely bypassing the customary authorization bill. Republican staffers would not be invited to help.

That signaled at least temporary victory in the Dole-Warner fight to preserve independent action by Reagan on the weapons front. The Nunn authorization bill would have forced the president to abide by the ''narrow definition'' of the Anti-Ballistic Missile Treaty and to drastically reduce the intensity of nuclear weapons tests.

In the House version, even harsher restrictions are placed on the president. Nuclear limits written into the abandoned, unratified SALT II treaty are imposed. Still less acceptable is a provision limiting the new Midgetman strategic missile to congressionally tailored measurements. Limits on length, weight, circumference and diameter are specifically imposed on the Pentagon in what specialists call an unprecedented congressional intrusion into the president's powers as commander in chief of the armed forces.

The beginning of the end of the debilitating Iran-contra hearings would seem to be the right time for the Reagan presidency to take the offensive, even on a modest level. The paramount issue is presidential prerogative -- so often the sustaining lifeblood of the republic.