A move by the Trump administration to suspend the federal gasoline tax would offer only modest relief to U.S. drivers socked by soaring fuel costs, according to tax and energy experts.

President Donald Trump told reporters on Monday that he would support temporarily suspending the federal gas tax “until it’s appropriate.”

Lawmakers from both parties have pushed for a gas-tax suspension, saying it would provide much-needed relief for families and businesses that rely on their cars and trucks to get to work and school an...