Delta Air Lines has had informal discussions with United Airlines about a marketing alliance, which would marry two powerful route systems but also raise antitrust issues.

A spokesman for Atlanta-based Delta declined to comment specifically about a potential United linkup but acknowledged the carrier is looking at various options."We've talked to numerous carriers," spokesman Bill Berry said. "We've approached them, and they've approached us."

It's known that a Delta-United alliance, in which the carriers sell seats on each others' flights and offer connections, is among scenarios Delta's strategic planners have been studying since the airline's failed effort to buy Continental this past winter.

Speculation about such an alliance was fueled by a Bloomberg News report that cited a United pilots union analysis suggesting Delta might seek a partnership. The pilots report said Delta stands to lose domestic market position from the pending alliance between Northwest and Continental, and "may attempt to initiate some activity" in response, with United its most desired target.

PaineWebber analyst Samuel Buttrick noted that United and Delta account for 36 percent of U.S. airline traffic. An alliance would combine United's strength in the Midwest, West and Asia with Delta's in the East and Europe.

Delta operates one of several national "hubs" at Salt Lake International Airport and is the city's dominant air carrier.

It is also one of the city's largest employers, with 4,500 people working in or out of the city. In February, Delta became the official airline of Utah's 2002 Winter Olympic Games.

Although United's closest hub to Utah is in Denver, it is still a major air carrier for Salt Lake air travelers.

"While the direct overlap may not be problematic from an antitrust standpoint, the overall scale of the deal might be," Buttrick said. Federal regulators have yet to approve the Continental-Northwest alliance, Buttrick noted, and the political climate has shifted against airline moves that could be viewed as anticompetitive.

But if the Northwest-Continental deal gets the green light, some airline watchers say regulators would be hard-pressed to stop partnerships among the remaining big airlines, with Delta-United and American-US Airways as possible pairings.

On the other hand, Delta Chief Executive Officer Leo Mullin, following the failed bid for Continental, downplayed the strategic virtues of alliances, as opposed to mergers, because the two partners remain independent with separate interests and strategies.

A United spokesman declined to comment, while a spokeswoman for the carrier's pilot union said the report cited by Bloomberg was "speculative in nature."