WASHINGTON — FROM liberal internationalists to hawkish conservatives, a chorus of influential voices in Washington is suggesting that American intervention in Syria would also do serious damage to Bashar al-Assad’s close ally, Iran.

Military action in Syria would demonstrate, so the argument goes, that America is serious about enforcing its red lines. Impressed and crestfallen, Iran’s recalcitrant mullahs would scale back their nuclear zeal and conform to international nonproliferation agreements.

However, given the fact that any intervention by the Obama administration is likely to be tentative and halting, rather than an overwhelming show of military force, it is not likely to end Syria’s civil war or intimidate Iran’s rulers.

The sort of intervention needed to bring about a decisive rebel victory would require more than no-fly zones and arms. It would mean disabling Mr. Assad’s air power and putting boots on the ground. America would have to take the lead in organizing a regional military force blessed by the Arab League and supported by its own intelligence assets and Special Forces. After that would come the task of reconstituting Syria and mediating its sectarian conflicts. As the war in Iraq painfully demonstrated, refashioning national institutions from the debris of a civil war can be more taxing than the original military intervention.