CAIRO – Millions of Egyptians are expected to vote today in a nationwide referendum on constitutional amendments, a poll that’s likely to lay bare the competing visions for democracy put forth since Hosni Mubarak’s ouster last month.

The youth blocs that emerged from Egypt’s revolution oppose the amendments, saying the old constitution is too flawed for quick fixes.

The biggest workers’ groups also are opposed. Presidential contenders including Arab League chief Amr Moussa and Nobel laureate Mohammed ElBaradei likewise urge “no” votes, preferring to start from scratch.

The “yes” camp, meanwhile, comprises some unlikely bedfellows. First, there’s the Muslim Brotherhood, the Islamist party and the most organized of Egypt’s opposition factions. Then come the remnants of Mubarak’s National Democratic Party, which stands a better chance of regrouping under an amended constitution. A few prominent leftists also are in favor of the changes, saying they would hasten the hand-over of power from Egypt’s military rulers to a civilian authority.

This is the topsy-turvy world of post-Mubarak politics, where alliances are fleeting, and voters are reeling from the unprecedented choices before them. This weekend’s vote, analysts say, will be an early gauge of the strength of the disparate blocs in Egyptian society.

Some 40 million people — roughly half the population — are eligible to vote, and turnout will be another barometer of Egyptians’ enthusiasm for the new political projects. Under U.S.-allied Mubarak, few people eligible to vote bothered to do so after years of rigged results.

The current constitution was suspended last month, leaving the Supreme Council of the Armed Forces in charge of the country and its caretaker government. But the military’s once-sterling reputation as a stable institution has been tarnished since Mubarak’s toppling, beset by allegations of torture and unlawful detention related to the clearing of protesters from a landmark square in downtown Cairo.

By most accounts, the military is pushing for the amendments to pass in hopes it quickly will be able to turn Egypt’s messy political affairs over to civilian rulers and get back to protecting the country during a dangerous security vacuum. The military wants today’s vote to be followed in short order by parliamentary elections and then a presidential one.

Despite their misgivings about the wisdom of amending a flawed constitution, some activists worry that voting down the proposed changes would only prolong military rule and cement the generals’ power in the drawn-out process of drafting a new constitution.Voter turnout will be another barometer of Egyptians’ enthusiasm for the new political projects.