Contract negotiations between the Air Line Pilots Association and United Airlines resumed here today as it became apparent that United's attempt to keep flying has not been as successful as management had hoped.

The talks adjourned around midnight and were to resume Tuesday at noon.

Helen M. Witt, chairman of the National Mediation Board, said during a lunch break at a suburban Chicago hotel that she thought there was ample reason for the parties to keep talking, but she did not indicate whether that was a positive or negative characterization. Spokesmen for the pilots and the company were also noncommittal.

Today's session between the parties was the first since the strike began after negotiations broke down early Friday.

Meanwhile, air travelers appeared to be coping with minimum difficulty on the fourth day of the strike against the nation's largest airline. Competing airlines, such as American, reported full flights, but even at Chicago's O'Hare International Airport this morning backups seemed no worse than usual.

The one problem area, according to United officials, is Hawaii, where 1,700 travelers holding United reservations will be stranded Tuesday, the officials said. United has been trying to persuade the Transportation Department to permit foreign airlines flying between Hawaii and the U.S. mainland to pick up those passengers, but Assistant Transportation Secretary Matthew V. Scocozza said, "So far, there seems to be plenty of U.S. capacity available. We're watching it closely."

United officials said they operated 212 flights Sunday, eight fewer than they had projected, and about the same number today. That is about 14 percent of United's normal schedule of 1,500 flights daily.

Monte Lazarus, United's senior vice president for external affairs, conceded that the airline was surprised that almost all of 500 newly trained but not hired pilots have respected the ALPA picket lines.

United offered those pilots jobs after ALPA struck, Lazarus said, but "most of them did not" cross picket lines. United is hiring replacement pilots and has an unknown number in training at its flight operations center in Denver, but it will be two to three weeks before the first of these will be qualified on United's procedures and planes.

Lazarus said United can operate 212 flights daily for the indefinite future and that with 75 percent of the seats filled, as was the case Sunday, "we were still the nation's sixth-largest airline."

The only issue on the bargaining table is United's desire to hire new pilots at a lower wage scale than current pilots receive. The argument is over how long two wage scales should be maintained before merging. United wants 20 years; the pilots have offered eight.