The crash of the Northwest Airlines jetliner in Detroit was the ultimate disaster for the Minneapolis-based company that has been battling a series of labor and service problems since its merger with Republic last year.

There were no indications yesterday that the carrier's labor troubles or recent incidents of vandalism played a role in the crash that killed at least 154, officials said.

Since Northwest's parent company, NWA Inc., acquired rival Republic Airlines for $884 million, the airline has been plagued by difficulties ranging from lost bags to disputes over pay scales.

Northwest also suffered losses in the first quarter of this year as a result of expenses related to the merger, but it since has doubled earnings in the second quarter.

But other problems have dogged Northwest management as it attempts to meld work forces, routes and equipment into one of the nation's largest airlines.

"It is an incredible mess," said one industry source, who suggested that complaints to the government about Northwest service have soared because the airlines' unions are sabotaging the complaint process. Last month, Northwest jumped to second in the number of passenger complaints filed against it, surpassed only by Continental Airlines, which has had service-related problems since it acquired several other airlines.

As with many of the airlines that have merged since deregulation, there have been battles at Northwest over union representation, pay scales and seniority lists.

"These things are traumatic, but you have to integrate these people into one work force," said John Galipault, who runs a nonprofit aviation safety hotline. "It's not easy."

Northwest and Republic pilots are arbitrating seniority rankings that will determine crucial issues such as pay, benefits and aircraft flown. In the meantime, Republic pilots fly Republic aircraft -- mostly DC9s and Boeing 727s -- while Northwest pilots fly Northwest equipment -- Boeing 727s, Boeing 757s, DC10s and Boeing 747s. In yesterday's crash, the plane was a former Republic aircraft.

In the case of mechanics, who are represented by the International Association of Machinists and Aerospace Workers, training is taking place so mechanics from each airline can service the other's aircraft.

For both groups, there have been problems with inequities in pay scales since the merger.

Northwest did not return telephone calls yesterday seeking comment on how these disputes are being resolved.

So turbulent have been many of the mergers in the airline industry from the labor point of view that the National Mediation Board, which mediates labor disputes and decides issues of union representation, has issued new procedures for how such matters are handled in mergers and acquisitions.

"We felt that there was a vacuum that we had to step into to prevent chaos in the sifting out of representation issues that result from a merger," said Helen M. Witt, chairman of the National Mediation Board.

Airlines will now be expected to file merger proposal information with the board as well as with the Transportation Department. "We will work with them through the planning stages instead of after the fact," Witt said.

Northwest also has had to contend with what it considers work slowdowns that have delayed flights. Though Northwest Chairman and Chief Executive Officer Steven Rothmeier has complained publicly about mechanics and baggage handlers staging slowdowns, union leaders have disputed the claim.

But more serious than consumers griping about lost bags and delayed flights are incidents of vandalized aircraft -- acts that the airline has called "nuisance" activity that have not affected aircraft or passenger safety.

One incident, for example, involved the severing of a wire leading to a cockpit warning light and horn that signals whether the nose wheel is down and locked during landing.

The airline reportedly has responded by offering rewards for information about the incidents. The Detroit Free Press has reported that the airline has brought in security guards to check minor acts of vandalism on equipment.

No evidence has been found that labor problems or vandalism played a role in the crash of the jetliner in Detroit late Sunday. "I don't see any connection," Robert Gibbons, a Northwest spokesman, told United Press International yesterday.

Since the end of last year, the Federal Bureau of Investigation has been looking at several incidents of vandalism at Northwest's ground facilities in Detroit and Minneapolis. The Federal Aviation Administration also has stepped up inspection surveillance.

"We're still very much involved in the investigation," said FBI spokesman Byron Gigler in Minnesota.