A federal mediator working to avert a second strike against financially troubled Pan American World Airways said both sides were "anxious to reach an agreement" as a deadline neared. Union officials said the main issue was preservation of flight attendants' jobs in light of the airline's desire to staff flights between international points with foreign nationals. They would not be covered by a union contract, an official said, and would be paid much less than union members. A spokesman said flight attendants and pursers make between $23,000 and $27,000 a year, assuming overtime. He said the foreign nationals would make from $225 to $773 a month.