BAGHDAD — Billed as a key test of Iraq’s nascent democracy, Iraqis fear today’s parliamentary election will lead to a protracted period of uncertainty as the winners and losers try to cobble together a new government — even as American forces prepare to go home.

None of the main political coalitions is expected to win an outright majority, which could mean months of negotiations and more violence despite hopes the balloting will boost efforts to reconcile Iraq’s divided ethnic and religious groups.

Iraq’s second nationwide election for a full parliamentary term comes at a vastly different time than the first in December 2005.

The U.S., which has lost more than 4,300 troops in the nearly seven-year conflict, has fewer than 100,000 troops in the country and their presence on the streets has all but vanished. The monthly American death toll has plummeted.

Overall violence is down dramatically, although attacks continue and insurgents have threatened voters.

A car bomb targeted Iraqi and Iranian pilgrims in the Shiite holy city of Najaf on Saturday, killing at least three people, including two Iranians, and wounding more than 50, officials said.

The balloting for a new 325-seat legislature has been billed as a major step in Iraq’s democratic evolution. Iraqis hope it will help them achieve national reconciliation at a time when the United States has vowed to stick to President Obama’s timetable that calls for the withdrawal of combat forces by late summer and all American troops by the end of next year.

But many observers have predicted it could take months for rival factions to form a new government. The bloc with the most votes will be able to nominate a prime minister but is probably going to need support from others to gain a majority due to the fractured nature of Iraqi politics.

Prime Minister Nouri al-Maliki’s government will stay in place until the new government is formed but on the practical side, not a lot of work may get done as ministers who are worried about retaining their jobs or scrambling for new ones lose focus on the day-to-day running of the government.

The instability also would leave the door open for more violence as political groups that don’t get what they want at the negotiating table take to the streets.

“This is a cause of considerable concern because there would be a kind of a vacuum,” said Adnan Pachachi, the elder statesman of Iraqi politics who is also running for parliament. “It is in everyone’s interest to try to form a government very soon.”

The vibrant political campaigning has seen large-scale rallies, town-hall style meetings and campaign posters and television ads that blanket the city and the airwaves. More than 6,200 candidates are vying for a seat.

Al-Maliki heads the State of Law Coalition, a largely Shiite group that presents itself as nonsectarian but is dominated by the religious Dawa party. Al-Maliki has risen to popularity as violence has diminished but his image has been tarnished by the government’s inability to stop large-scale bombings in Baghdad or provide basic services like electricity.

The U.S.-backed leader also faces intense pressure from his former Shiite allies — the Supreme Iraqi Islamic Council and the Sadrist Trend led by anti-American cleric Muqtada al-Sadr — who are closely allied with Iran and have teamed up in a separate alliance.