WASHINGTON — Jeffrey D. Zients, a multimillionaire entrepreneur and management consultant, joined the Obama White House in 2009 with a mandate to streamline the federal bureaucracy. A year later, he issued a prescient warning.

The government “largely has missed out” on the information technology revolution, Mr. Zients said in a 2010 internal memo. “I.T. projects too often cost hundreds of millions of dollars more than they should, take years longer than necessary to deploy and deliver technologies that are obsolete by the time they are completed,” he wrote.

These days, Mr. Zients is witnessing that ineptitude up close as the emergency fix-it man charged with righting HealthCare.gov, the bungled online marketplace for medical insurance. He is to become President Obama’s top economic adviser in January, but first he is leading the so-called tech surge to haul HealthCare.gov into the 21st century. Ignoring friends who told him not to get mixed up in the website fiasco, Mr. Zients (pronounced ZYE-ents) promises it will run “smoothly for the vast majority of users” by the end of November — a schedule considered highly optimistic.

Mr. Obama’s reputation, and the electoral fortunes of Democrats, could hinge on the work of Mr. Zients, a man who has no hands-on technology experience — although he has advised health care companies on business practices. In the universe of experts who might have been called in for rescue work, Democrats close to the administration say, there were others perhaps more qualified than Mr. Zients, but he was the best of those Mr. Obama and an insular White House were comfortable with.