This was the biggest weekend in commercial aviation history, with more than 3 million people boarding airplanes across the country.

The combination of an escalating number of new discount fares and a pilots' strike that has all but grounded Northwest Airlines had led to several airlines also setting individual passenger records.

United Airlines, for example, set highs for passengers traveling in one month (June, 3.98 million), one week (that beginning June 25, 1.02 million) and one day (last Friday, 166.107 people). The weekly total marks the first time any airline carried more than 1 million people in one week.

Eastern Airlines also reported several records, including the best six-month record in its history. During the first half of 1978, Eastern reported 18.3 million boardings, up 17.4 percent from the same period last year.

And last Friday, Eastern said, its 136,158 passengers represented a single-day record for the 50 year-old airline. The Eastern shuttle from Washington to New York had to add 38 planes on Friday - in addition to the scheduled 15 - to take up the extra business. In addition, June figures were running a whopping 34.4 percent ahead of last year.

"It appears that America's sudden filing at air travel could be turning into a lengthy phenomenon," said Russell L. Ray. Jr. Eastern's senior vice president for marketing. "It's already lasted four solid months and from our advance bookings it should continue through the summer."

He attributed much of the increase to the new discount fares, but said that business travel was also showing a steady increase over last year.

Dan Hankin of the Air Transport Association said that the 3 million weekend travelers made this "the biggest weekend in aviation history."

"We have seen during the first five months of this year that traffic is going up almost 2 million a month," he said. The first five months of 1978 saw 15.5 percent more passengers than the same period of 1977, while May 1978 traffic was up 18.8 percent over May 1977.

Another crucial barometer of airline profitability as well as volume increase is what is known as the load factor - the percentage of seats taken on any given airplane at takeoff.

The historical average load factor has been about 55 percent. According to Hankin, this year's average load factor has been 62.1 percent, compared with 54 percent last year.

"And now we are running into the high 70s, with each month higher than the next," he said. "One airline, Allegheny, even hit 84 percent last month."

Hankin said that there "is no question that lower fares are a major part of the increase." He said that more than 40 percent of all air travelers today are using discount fares of one type or another.

At the United ticket counters at Washington's National Airport, where five striking Northwest Airlines employes are moonlighting to help handle record business, long lines were present much of the weekend. One of the major problems caused by the rapid increase in the number of available fares is the increased time it takes to book a flight for a passenger.

"We have to explain a whole range of fares now," said United customer service supervisor Richard Thieleman. "It makes three times as long to process a ticket than it did a year ago."

"And," he added, "we get a lot of weekend shoppers here, who come by to pick up reservations that have to be purchased in advance for the discount fare. We also get a number of people who come down because they can't go through on our telephone lines."

Members of Congress and their staff people are among those scrambling to get tickets on already-booked flights. "There just isn't anything I can do for them," Thieleman says. "We have planes that hold 127 with waiting lists of 100 to 120. United planes leaving National Airport are averaging between 75 and 80 percent load factors."

"You ought to see the lines of people holding standby tickets for fully booked flights," says United ticket agent Bill Dearcangelis. "They remind me of expectant fathers - they pace nervously and keep looking over our shoulders."

Consumer activists have long claimed that airline business would increase dramatically if fares were lowered. Airline officials, however, fearing widespread economic deregulation of their industry, had, until recently, disagreed. Because of the record number of travelers in the air today, however, many airline executives have changed their tune.

"Lowered fares have caused people to take trips," said United Airlines official Tony Schoepf. "Volumes have been of such a nature as to offset the drop in yield on each ticket. But I don't think anyone knows the potential."

However, at least one consumer advocate is not entirely happy about the way things are going.

Ralph Nader helped the consumer cause considerably when he successfully sued an airline for "bumping" him off a flight on which he had reserved a seat (the airline got caught giving out too many confirmed seats - a regular industry practice). But Nader himself was a recent victim of the sudden upsurge in passenger travel.

According to one United Airlines employe, Nader asked permission to board a flight he could not get a reservation for in an attempt to buy a ticket from an already seated passenger.

The airline refused.