CHICAGO — United Airlines is pondering its strategic options as stalled talks between Delta Air Lines Inc. and Northwest Airlines threaten other linkups, including a potential tie-up between the Chicago-based carrier and Continental Airlines, sources said.

Talks between United and Continental have halted while the airlines wait to see whether pilots at Delta and its favored partner, Northwest, can resolve a deep split over seniority, sources said.

"At the end of the day, the decision at the Delta-Northwest merger is going to determine whether there are other mergers in the industry or not," said Julius Maldutis, president of Aviation Dynamics Inc., a New York-based consulting firm.

The complication for United is that it can't secure a Continental deal until after Delta and Northwest tie up because Northwest holds a "golden share" in Continental that gives it the power to nix any merger between Continental and another carrier. Northwest forfeits that right if it achieves a merger of its own.

While United waits, it is looking more intently at Delta, whose holdings would also fit well with United's Midwest and West Coast strongholds and its Pacific Rim network, sources say. Like Houston-based Continental, Delta has a strong network across the Southeastern U.S., a major hub in New York and a wide array of flights across the Atlantic.

But every feasible option is being scrutinized by airline executives as they mull consolidation that is unprecedented both for its scope and the scrutiny of the process.

Continental also held exploratory talks with American Airlines, a source said. In January, Delta's board considered proposals from both United and Northwest before settling on Northwest, the former employer of Delta's chief executive, Richard Anderson.

Driving the urge to merge is the precipitous plunge in airline stocks over the past year, record-high oil prices and fear that the industry may be headed for another downturn. Executives also want to wrap up deals by spring so they'll be reviewed by the Bush administration.

But airline mergers tend to be complex, messy and easily derailed, analysts said. Momentum could quickly shift against industry-wide consolidation if Delta and Northwest pilots aren't able to agree on a framework for seniority. The pecking order affects almost every aspect of their working lives, from income to the aircraft they fly.

For starters, Delta would likely still encounter bitter fighting among pilot groups if it turned to Northwest instead of United, Maldutis noted.

Both groups belong to the Air Line Pilots Association. Both have tough union leaders.

"If there's no seniority agreement between Delta-Northwest, there's not going to be a seniority agreement between Delta-United," Maldutis predicted.

However, the boards of carriers eager to merge could decide to move ahead and resolve seniority issues later, as has traditionally been done in the past, countered Roger King, airline analyst with CreditSights Inc.

"You just move on," he said. "Their contracts are pretty iron-clad. It's well-defined (by ALPA) what happens in a merger between two pilot groups."

Other sticking points to a Delta-United deal are the questions of brand and corporate headquarters.

Anderson, Delta's CEO, told employees in a memo last fall that neither were negotiable: Delta wouldn't agree to a deal unless its brand and Atlanta headquarters survived.

That means United would have to give ground on both issues to reach a deal, sources said.

Representatives for American, Continental, Delta and United would not comment.