Comcast Corp. has courted NBC Universal for months, but the companies would need to take a long detour to Washington before they make it to the altar.

Starting Sunday, Vivendi SA had an option to sell its 20 percent stake in NBC Universal. Majority owner General Electric Co. is expected to buy it and then sell a 51 percent stake of the entire NBC Universal unit to Comcast, which serves about a quarter of the nation’s subscription TV households.

The Obama administration would face its first media megadeal. Regulatory approval is expected to take from six months to more than a year.

The government is unlikely to derail the tie-up, legal experts and others familiar with the matter say. But regulators would likely impose restrictions to mitigate potential harm to rivals and consumers. Those restrictions could wipe out some of the benefits of the deal, which if completed could be announced as early as this week.

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