Negotiators for United Airlines and the machinists union are scheduled to resume bargaining here today in an effort to end the five-day-old strike against the nation's largest airline.

Negotiations scheduled for yesterday were delayed because union bargainers had difficulty getting flights here from their office in San Francisco.

Meanwhile, United announced it was cancelling flights through April 12 in an attempt to give the traveling public enough time to try to make other arrangements during heavy Easter holiday travel.

United also announced that its remaining 22,000 working employes-nonunion and management-would go on half salary beginning today. Some 18,600 mechanics and other ground workers are on strike, and another 13,780 nonstriking union employes were laid off earlier.

The airline was struck at midnight Friday by the International Association of Machinists and Aerospace Workers after its members voted overwhelmingly to reject a second proposed contract with the company.

The tentative agreement had been worked out in three days of marathon bargaining under the auspices of the National Mediation Board after the first tentative agreement was rejected March 15. Federal mediator Robert O. Harris, who acted as chief mediator during the last go-around, will resume that role today.

The rejected agreement included wage increases averaging 31.9 percent over three years in addition to cost-of-living adjustments and other benefits.

Sources close to the negotiations say the prevailing view is that the contract is not subject to President Carter's anti-inflation guidelines because it is being patterned after Trans World Airlines contract signed with the union last fall before the guidelines were announced.

Although all scheduled United flights are grounded, the airline said yesterday that management personnel would fly about a dozen one-way flights this week from Hawaii to the mainland to take care of passengers stranded because of the strike.

A United spokesman said between 3,000 and 4,000 travelers with confirmed United reservations may have been unable to reschedule flights on other airlines, parimarily because they are part of large groups travelling at group rates. United normally supplies half of all incoming and outgoing flights to the Hawaiian islands from the U.S.

In another development, flight attendants for Pan American World Airways told the flag carrier they would go on strike next Sunday if a contract is not agreed on. The 4,500 members of the independent union have been flying without a contract for 17 months.

The union said a 30-day "cooling off" period imposed under National Mediation Board procedures will have expired by Sunday, making the union free to strike.

A spokesman for Pan Am said airline officials hope a contract can be worked out. Negotiations were held yesterday here with federal mediator Roland K. Quinn serving in an informal capacity, and are expected to continue today.