Chicago ? Investors reacted optimistically Monday to United Airlines’ tentative cost-cutting agreement with flight attendants, pushing the carrier’s stock higher despite analysts’ renewed predictions of a bankruptcy filing.

Shares in United parent UAL Corp. rose 29 cents, or 9 percent, to close at $3.57 on the New York Stock Exchange after initially shooting to $3.85.

United said the agreement for $412 million in wage concessions from its 26,000 flight attendants over 5 1/2 years is in line with the airline’s plan to achieve $5.8 billion in labor cutbacks.

“This is indeed another very significant step in the company’s efforts to successfully re-structure out of court,” chairman and CEO Glenn Tilton said Monday in a message to employees.

Two critical issues remain unresolved, however: whether the airline’s 36,000 machinists will agree to significant cost concessions, and whether the overall cuts will be enough to gain a much-needed $1.8 billion government loan guarantee.

The Air Transportation Stabilization Board must approve the loan guarantee. As United officials headed for more meetings with the board this week, Wall Street analysts expressed doubt about the depth of the airline’s proposed cost reductions.

Jamie Baker of J.P. Morgan said the lowered wages and other cutbacks won’t significantly reduce United’s high cost structure, as the government panel has demanded. Baker also said the cash-tight carrier hasn’t provided convincing evidence that sinking revenues will recover.

“With an ATSB decision reportedly weeks away, the clock isn’t merely ticking, it has begun to chime,” Baker said in a note to investors.

James Higgins of Credit Suisse First Boston said it was unlikely that the board would approve the loan guarantee. He reiterated the widely shared belief that a Chapter 11 bankruptcy filing is “by far the most likely outcome.”

United faces a Dec. 2 deadline for the repayment of $375 million in aircraft-backed loans, as well as a $70 million payment to the machinists union for retroactive wages due Dec. 15. It has warned of a bankruptcy filing if it doesn’t get the government loan guarantee.