BOSTON--Lured by the lowest fares in 28 years, 31,500 people crossed picket lines over the weekend to take the Eastern Airlines shuttle between Boston, New York and Washington, airline officials said yesterday.

But airline ticket officials at Logan International Airport had to tell some 200 passengers last night that they would have to wait until morning to get back to New York, because the evening's flights were booked solid.

In a gambit to maintain customer loyalty despite a strike-induced bankruptcy, Zastern cut the price of a weekend shuttle ticket to $12, the original fare that the airline charged when it started the shuttle in 1961.

Stranded passengers were told to show up at the Eastern terminal at 5:30 a.m. today, when the first shuttle is slated to leave Logan. People with no pressing matters had virtually all day to get on an airplane, but those who had to be at work this morning were in a bind.

"I certainly expected to get on a later flight," said Terianne Tapia, who was up from New York to visit her boyfriend in Boston. "It's a bummer. I have to be at work at 9 a.m."

But Eastern officials were more optimistic.

"It's going great," Marilyn Rogers, deputy director of Eastern services at Logan Airport, said yesterday afternoon. "We're just packing them on."

On Monday, the fares jump to $49. But that is still significantly lower than the regular price of $69 to $99.

Eastern plans to honor any $12 return tickets held by stranded passengers through Friday.

John Siefert, Eastern's vice president for the shuttle, said 8000 people flew between the three cities Friday, 11,000 Saturday and 12,500 Sunday.

In Boston, there were so many people lined up for seats Sunday morning that the airline added an extra flight at 8 a.m., an hour earlier than usual. Most of the subsequent hourly departures were sold out.

Striking machinists and pilots maintained a 60-person picket line at Logan but did not interfere with people crossing it, said Edward Imondi, business agent for Local 1726 of the International Association of Machinists in Boston.

"We're trying to be non-abrasive," he said. "You look them in the eye, and that's enough."

The strike, which began March 4, has idled 8500 mechanics, bag handlers and ground crews at the nation's seventh largest airline.

A decision by Eastern pilots to honor the picket lines prompted the airline to file last week for protection from creditors under Chapter 11 of the federal bankruptcy code. Officials have said it is losing about $4 million a day.

But some strikers are skeptical of the airline's claim to be out of money.

"Selling tickets for $12, they're losing money hand over fist," said Imondi. "How can you give your product away like that and then claim to the court you're bankrupt?"

Eastern also said yesterday it had resumed service between Miami and 13 Latin American cities. Non-stop service between Boston and Washington is slated to resume Thursday. But it remains unclear how long the airline can continue to operate while its losses mount.