Adds analyst comment, paragraphs 10-12

By Nandita Bose and Timothy Gardner

WASHINGTON, May 11 (Reuters) - President Donald Trump said on Monday he backs reducing the 18-cent federal gasoline tax as U.S. fuel prices shoot higher due to the Iran war.

Waiving the tax requires Congress, currently controlled by Trump's fellow Republicans, to pass legislation.

"Yeah, I'm going to reduce," Trump told reporters on whether he would suspend the tax. Asked how long he would suspend the tax, Trump said in the Oval Office, "till it's appropriate."

U.S. Senator Josh Hawley, a Missouri Republican, said on X that he is introducing legislation on Monday to suspend the gas tax.

In March, some Democrats including Senator Mark Kelly of Arizona first proposed suspending the tax, which generates about $2.5 billion per month in road funding, until October. Since 2008, more than $275 billion - including $118 billion from the 2021 infrastructure law - has been shifted from the general fund to pay for road repairs.

Trump told CBS earlier on Monday that a bailout plan for airlines, which are struggling with surging jet fuel costs, had not "really been presented" and that "the airlines are doing not badly.”

U.S. states also tax gasoline, with Indiana, Kentucky and Georgia moving to make cuts to give consumers some relief at the pump.

Gas prices have risen since the war began on February 28, and as Iran effectively keeps closed the Strait of Hormuz, a chokepoint through which 20% of the world's oil traditionally passes. Gasoline prices in the U.S. averaged $4.52 a gallon as of Monday, the highest since 2022, when the average peaked at $5.01, according to AAA motor club.

Rising fuel costs, which also stand to boost the price of groceries and other goods, are a vulnerability for Trump and Republicans who are trying to hold control of Congress in the November elections. Trump said he knows the tax is only a small percentage of the overall cost of gasoline for consumers, "but it's still money."

CONSUMERS WILL BARELY NOTICE

Trump has taken a number of other actions meant to calm energy prices such as loaning crude from the Strategic Petroleum Reserve and waiving a shipping law known as the Jones Act that makes it easier to move oil, fuel and fertilizer around the United States.

Bob McNally, the founder and president of Rapidan Energy Group who served as White House energy adviser to former President George W. Bush, said waiving the tax may not make much difference if the war continues to clog shipments in the Middle East.

"If the federal gasoline tax is suspended but the Strait of Hormuz remains closed, consumers will barely notice as pump prices continue to march higher," McNally said.