Those routine take-off delays that the air controllers' strike brought to some air routes will not be lengthened significantly by the Christmas rush, federal and airline officials predict. But travelers still will face traditional holiday jam-ups in ticket lounges and airplane cabins.

Official optimism grows out of this year's experience on the day before Thanksgiving, traditionally the busiest day of the year at U.S. airports. Extra flights were held to a minimum and the reduced controller workforce moved the traffic without unusual disruption, according to the Federal Aviation Administration. Officials say they can do it again for Christmas -- if the weather cooperates.

As with every Christmas-New Year season, weather is the unknown factor. If a big snowstorm blankets the Northeastern states, for instance, flights could be tied up in much of the country, regardless of how many controllers are on the job. Thanksgiving travelers were lucky to have good weather.

Strike-related delays occur primarily at peak hours when controllers are asked to handle too many planes at once and begin ordering some of them to wait on the ground. These delays should not grow significantly during the holidays, the FAA says, because the number of planes in the air will not increase much.

Increased demand for seats will be met by flying more wide-bodied planes and flying planes fuller than usual, airline spokesmen say. November's load factor for domestic flights -- average percentage of seats filled -- was 54 percent. "We have a lot of capacity up there, a lot of seats that haven't been used," said Jim Ashlock, spokesman for Eastern Airlines.

Checks with airlines yesterday indicated many flights were full or getting close to it,

There are fewer extra flights this year for two reasons: air travel is less popular due to the economic recession, and in order not to overload the control system, the FAA gives permission for extra flights primarily at off-peak hours, which is precisely when airlines don't want to fly them.

Even if planes leave no later than usual, passengers will find that they spend longer getting to the departure gate, as big holiday crowds build up at ticket, security and baggage facilities designed for normal weekday traffic.

Janna Aynes of the Dallas-based Airline Passengers Association recommends that passengers get to the airport at least one hour before their flights, to allow extra time for slow-moving holiday lines.

Those who booked well in advance should check with their airlines from home to make sure their flights weren't eliminated when schedules were cut back due to the strike, Aynes said. She also cautioned that travelers may find that airport parking lots which normally have empty spaces are filled to capacity.

Departure delays have become a way of life on certain air routes since the Aug. 3 walkout. In general, they are caused by staffing shortages in the regional "en route" centers that guide airplanes between airports.

Delays are most frequent for peak-hour flights in and out of airports at New York, Chicago and Dallas-Fort Worth, but can occur anywhere in the country. Even flights that don't land at those three cities' airports can be held back on the ground while awaiting permission to cross airspace controlled by the enroute centers serving them.

Business travelers who day after day spend 30 minutes in planes parked at LaGuardia waiting for take-off may be skeptical, but the FAA says that delays are not as common as it seems.

In the first 20 days of December, according to a spokesman, an average 425 of 21,000 daily flights in the U.S., or about 2 percent of the total, were delayed 30 minutes or more. For all of December last year, the figure was 179 of 26,500 flights daily, about 0.7 percent.

Airlines could devise schedules with virtually no delays if they chose to, by spreading out scheduled departure times into the quieter hours of the day, FAA officials say. But competition and the desire to advertise flights for peak hours -- even if they consistently are 30 or 60 minutes late getting off -- have led carriers to use schedules with built-in delays, the officials say.

The FAA has ruled out rehiring 11,500 strikers who were fired for striking and predicts that traffic won't fully return to normal until 1984, when a new corps of fully trained controllers will be in place. Traffic is now holding at about 75 percent of prestrike levels, the FAA says.