BAGHDAD  Iraq’s independent electoral commission on Thursday barred about 500 candidates from running in parliamentary elections in March, among them an influential Sunni Muslim politician, in a decision that could stoke sectarian tensions here and deprive the vote of crucial legitimacy in the eyes of part of the electorate.

The decision could undermine what many viewed as a key accomplishment of the political process here: agreement by nearly all Iraqi factions to take part in the vote, unlike previous elections that were boycotted out of fear of insurgent violence or in protest of American involvement.

Among those barred were the defense minister, Abdul-Kader Jassem al-Obeidi, and Saleh al-Mutlaq, a Sunni who is the head of the National Dialogue Front.

Mr. Mutlaq’s group, in alliance with Ayad Allawi, a former prime minister, had emerged as a leading force in predominantly Sunni provinces, which were underrepresented in the last parliamentary vote, in 2005. Depending on how many seats they secured in Parliament, the alliance could have had a say in choosing Iraq’s new prime minister.