WASHINGTON — The Obama administration said Friday that it would fix problems in the federal health insurance marketplace by Nov. 30, just two weeks before the deadline to sign up for coverage to replace health insurance policies being canceled because they do not meet new federal standards.

To help meet that schedule, the Obama administration, in an abrupt shift, named a “general contractor” on Friday to oversee changes to the troubled Web site of the federal marketplace.

Such a condensed time frame raises the question of how hundreds of thousands of people whose current policies do not comply with the health law will obtain new coverage in time, and how millions who may qualify for subsidies will enroll. Some experts predicted a groundswell of demands from Congress and elsewhere to delay the deadlines.

Jeffrey D. Zients, President Obama’s troubleshooter on the project, said the general contractor, Quality Software Services Inc., a unit of the UnitedHealth Group, would now “manage the overall effort,” like a general contractor on a home improvement project. Notably, that company had a role in developing one of the most troubled components of the marketplace, which helped verify the identities of those registering.