The hardiest of those taking advantage of Pan American World Airways' new low fare Boston to Amsterdam flight - the cheapest in aviation history - began pouring in from around the nation on Wednesday to be the first on last night's maiden trip.

Scattered near the standby ticket counter at Logan Airport on sleeping bags and foam rubber pads, they whiled away the hours watching television and hunched over scrabble boards and newspaper crossword puzzles.

PamAm initiated the new flight yesterday - the day its Boston-to-London flight was scheduled to end - as an alternative to pulling out of this city, William Cowden, Pan Am's regional managing director said.

The Boston-to-London service was shut down because of an 11-month old international aviation agreement with England which allows the United States to have two domestic airline flights from two cities on the London route. Last week President Carter designated Los Angeles as the second city along with New York.

Rather than end its European flights from New England, the company on Tuesday announced a "great innovation" - a no-frills service for $99 one way to Amsterdam and $50 return.

During July and August the fare will be hiked to $279. At the end of the three-month experiment, Pan Am officials said they will decide whether to continue the daily service.

This month's $149 round-trip fare only covers the direct costs to the airlines, said William H. Waltrip, executive vice president for marketing and services. A profit is expected when the ticket price jumps next month.

"I think we can make Amsterdam the hub to Europe," Cowden said as dozens of reporters and cameramen swanned around him and the crowd of travelers. "And the low fares will tap a whole new strata of people who wanted to go but couldn't afford it."

People like Steven Watts, 25, a postal employe from Lawrence, Kan., who said, "When I heard about it I thought, 'my God, I've been trying to get the money to go Europe for years but I couldn't do it.' And then here it is - my trip to Europe."

Robert Lena, a 33-year-old candidate for the Maine House of Representatives said he didn't even mind not being served a meal on the flight, "No airline in the world can cook a $400 dinner - I would have been crazy not to come."