CHICAGO — United Airlines is expected to ground dozens of its least fuel-efficient aircraft, including Boeing 747 jumbo jets, as part of sweeping cuts intended to help the carrier conserve cash and survive a daunting environment as a standalone company.

The Chicago-based airline intensified planning for the initiative as it cooled on a potential merger with US Airways in mid-May, say people familiar with its plans. United is expected to announce the cuts as early as today.

With the economy in a downdraft, capital constraints have made large-scale mergers largely unfeasible, prompting carriers like United to seek other ways to cut capacity in an effort to gain sufficient pricing power to cover rising fuel costs.

United plans to retire the workhorses of its domestic fleet: 94 older Boeing 737 jets, single-aisle planes that seat up to 123 passengers and shuttle over medium-range distances, people close to the company say.

United had already planned to ground 30 Boeing 737-500s, which seat just 108 passengers but burn as much fuel as the larger narrow-body jets that Boeing uses within North America.

But the nation's second-largest carrier now will phase out its 64 Boeing 737-300s, whose average age is approaching 20 years, sources said.

"Aging goes hand in hand with fuel inefficiency," said aviation consultant Robert Mann, president of R.W. Mann & Co. "At these fuel prices, more and more of the domestic network is uneconomic."

United is also preparing to park some of its largest jets, Boeing 747s that haul about 350 passengers and are primarily used for flights to Asia and Australia, sources said.