The Teamsters union will launch a worldwide strike against Pan Am Corp. on Sunday, union officials reiterated on Thursday.

However, the troubled carrier pledged to remain fully operational if the

4,500 Teamster members walk out.While Teamsters union officials say their strike against Pan Am Corp. could cripple the troubled carrier within 24 hours, four other unions appear unlikely to support the walkout.

The scheduled strike would come at the end of a federally mandated 30-day cooling-off period in the union's dispute with the airline.

Pan Am spokeswoman Pamela Hanlon said the airline will remain fully operational if the Teamsters walk out.

She had no comment on a Teamsters claim that the carrier has begun installing armed guards throughout its facilities at New York's John F. Kennedy International Airport, the airline's main hub.

Obviously security is a top priority, Ms. Hanlon said. We are making preparations to deal with it, but we won't disclose what they may be.

The Teamsters say they have been in close contact with (Pan Am's) other four unions, and we believe they will be with us 100 percent. Those unions represent the pilots, flight attendants, flight engineers and transport workers.

But sources said there has not been a groundswell of support from either the flight attendants, pilots or flight engineers. A spokesman for the flight engineers said its members were advised to continue with their work assignments.

Jim Gannon, a spokesman for the 5,000-member Pan Am Transport Workers Union, said his group would vote Thursday on whether to support the Teamsters.

The Teamsters say they can shut down the airline system wide within 24 hours without the help of other unions. The Teamsters represents passenger reservation clerks, customer service workers and the workers who fuel the planes. You can't fly a plane without fuel, a Teamsters official said.

But Ms. Hanlon said the carrier has taken a number of steps to ensure it will not be shut down, including recruiting potential replacement employees over the past few weeks. Pan Am management also have been trained to perform some of the Teamsters' clerical functions.

Both Pan Am and Meredith Buel, a spokesman for the National Mediation Board in Washington, acknowledge that negotiations are still going on. The Teamsters, however, denied that any bargaining sessions have been scheduled, although the union is willing to talk.

Mr. Buel said the NMB has had a federal mediator in New York since Feb. 10 and added that mediation will be on going through the (strike) deadline and beyond if we have to.

Pan Am lost $462 million in 1986 and has said its loss for last year is expected to be well above $90 million.