Citing soaring fuel prices and high labor costs, the nation's third and fourth largest airlines filed for chapter eleven bankruptcy yesterday. Delta and Northwest are expected to join carriers United and US Air in using bankruptcy to cut workers' jobs, wages and pensions. A strike by mechanics and cleaners at Northwest is in its fourth week over company demands for over one billion dollars in concessions. The striking workers received both good and bad news this Tuesday, as the United Auto Workers donated 800,000 dollars to support the strikers and the company announced that it had begun hiring permanent replacement workers.