Republican and Democratic congressional leaders discussed the rescue plan at the White House with President Bush as United Airlines and the parent company of American Airlines said they would lay off about 20,000 employees each.
The latest announcements bring to more than 60,000 the number of job cuts announced in the airline industry over the past week.
US Airways has said it plans to lay off 11,000 employees, and Continental will cut 12,000 jobs. In addition, aircraft manufacturer Boeing Co. has said it might cut as many as 30,000 employees by the end of next year.
Bush called it a "shock" to the economy and said, "We're going to respond."
Of the four planes that were hijacked and crashed in last week's attacks, two were from American and two were from United.
The cuts at American amount to about one-seventh of its work force and will include layoffs at its Trans World Airlines and American Eagle commuter lines.
Analysts have warned that total layoffs could exceed 100,000, and industry officials fear the industry's financial losses could grow if passengers remain reluctant to take to the air again in the aftermath of last week's disaster.
Lawmakers could act as soon as this week on a $5 billion cash grant to the industry to cover losses suffered since the Sept. 11 attacks.
Action on $12.5 billion in loan guarantees could come within the next few weeks, aides said.
The $17.5 billion package has been reduced significantly from the $24 billion the industry had been requesting earlier this week. No longer included is about $7.8 billion in tax relief, which drew opposition in Washington.
"The terrorists have already scored a short-term victory with the closing down of [Reagan] National Airport," said D.C. Del. Eleanor Holmes Norton, a nonvoting House member.
"We must not give them any victory in the closing down of major airlines and the effect that would have on countless workers and communities," she said.
In addition to the 266 passengers and crew members killed in the four hijacked airliners, more than 5,000 people might have lost their lives on the ground in New York and at the Pentagon.
Delta Air Lines Chairman Leo F. Mullin told the House Transportation Committee that Congress should declare the terrorist attack an act of war so the airlines involved "would not be liable for the damage to persons and property on the ground."