PHOENIX, Ariz. -The jibes started as soon as the code name for the America West-US Airways merger talks leaked out in April.

Project Barbell, so named for the airlines' strengths on opposite coasts of the country, was quickly derided as Project Dumbbell. US Airways was bankrupt and the industry was bleeding badly.

The airlines silenced many critics when they unveiled $1.5 billion in financial backing for the deal in May, but the cheering section for the merger has never been big.

Whether the fan club grows or the boos get louder will be decided beginning this week. The new US Airways, billed as the first nationwide low-cost, full service airline, is set to debut Tuesday under cloudy industry skies.

The highly regarded America West executives who crafted the merger and will run the nation's fifth-largest airline have a tall order: they must get control of US Airways' unwieldy East Coast network; keep costs down; and successfully combine two large workforces. At stake are nearly 40,000 jobs, nonstop flights in hub cities, shareholders' money and more.

No one, including America West and soon-to-be US Airways CEO Doug Parker, says the merger is going to be easy. The industry's woes are well documented: sky-high fuel prices, competition at every turn, excess capacity and labor showdowns.

And the merger brings its own set of troubles: seniority battles among employees, possible culture clashes when East meets West and lingering losses and operational problems at US Airways.

The new US Airways will debut with one important thing on its side: a pile of cash, about $2.5 billion — higher than initial projections. That provides staying power in a time of projected heavy losses.

Not having enough cash was what almost sunk America West after the 9/11 terrorist attacks, and was a concern again this year when fuel prices spiked.

"We'll be finally in a position where we're financially secure and stable," said Scott Kirby, executive vice president of sales and marketing and the airline's merger point person.

The new airline also will have low costs. America West long has been in that camp and US Airways got there, painfully for employees, during two trips through bankruptcy court.

The list of headwinds facing the new US Airways, though, is long.

Mike Boyd, an aviation consultant in Evergreen, Colo., puts the old US Airways' operations at the top of the list. He noted that the airline recently told bankruptcy court officials it continues to have significant operating losses and will through 2006.

"That has to get stanched," Boyd said. "The challenge is what do you do to keep this thing alive?"

America West executives haven't revealed their strategy beyond saying they see big financial benefits from route restructurings and flight rescheduling. No major service changes have been announced in advance of the merger.

The other big challenge, one over which company executives have less control, is labor peace.

The airlines' pilots, flight attendants, mechanics, ramp agents and other front-line workers all are represented by unions. All will need to negotiate new contracts that cover employees from both sides.