As a soap opera, the perils of Pan Am has had a long run.

It may continue today when U.S. Bankruptcy Judge Cornelius Blackshear hears arguments on Pan Am's proposal to sell its prestigious London routes to United Airlines and on a motion to approve stop-gap financing that will carry it through until the route sale is completed.

Without those approvals, Pan Am is perilously close to running out of cash.

Chairman Thomas G. Plaskett declined to say how long the airline could last without the $150 million cash infusion. But he acknowledged that Pan Am Corp. was down to approximately $30 million when it filed for Chapter 11 bankruptcy protection on Tuesday.

"I'm sure we'll be making the case tomorrow that it's imperative that the court do it as quickly as possible," said spokesman Jeffrey Kreindler yesterday. "We're confident that it will be done."

Although no motions opposing the transaction and the interim financing had been filed as of last night, opposition to -- or at least questions about -- the transaction could come from at least three different sources.

Delta Air Lines Inc., which has tried to delay regulatory approval of the route sale, said last night it plans to file a petition relating to some of the assets involved in the transaction. Delta previously had said it was interested in acquiring the Los Angeles-to-London route that is part of the transaction.

Trans World Airlines Inc., which had proposed merging with Pan Am, may also have some objections. TWA Chairman Carl Icahn said he initially offered to buy the routes that were sold to United, and American Airlines Chairman Robert Crandall has said he believes the routes are worth more than the amount Pan Am realized in the $400 million transaction with United.

Both remarks could provide the basis for arguing that Pan Am's creditors might receive more money if the bidding were opened up for the routes.

The third possible source of questions may be the federal Pension Benefit Guaranty Corp. As the carrier's largest unsecured creditor, the PBGC may also want to assure itself that the United transaction represents the highest price obtainable.