NEW YORK (AP) _ First Interstate Bancorp sharply criticized BankAmerica Corp.'s defensive ''dismemberment'' earlier this year, but now it finds itself in the same boat - a restructuring that will cut the payroll, sell some operations and sharply pare loan dealings with the Third World.

The announcement came as Chase Manhattan Corp., the nation's second largest banking company, announced a further step in its year-old restructuring that will cut 1,000 jobs through an early retirement program.

First Interstate, the nation's No. 8 banking company, said Wednesday it also planned to trim about 1,000 jobs through layoffs. It also said it would divest some business operations and take steps to significantly distance itself from its outstanding Third World loans and other non-core lending.

It was the latest sign of the major retrenchment by the nation's bankers, who are cutting back in the face of rising overhead expenses, losses on bad loans and heightened competition for their traditional customers.

It also provided a clear statement by First Interstate, which has about $1.6 billion in outstanding loans to developing countries, that it had no plans to remain a major lender to the Third World.

''We are going to focus even more strongly on the retail customer, the middle market customer, and the large corporate customer with operations in our territory,'' said J.J. Pinola, First Interstate's chairman and chief executive.

First Interstate dropped an unwanted $3.23 billion buyout proposal for BankAmerica earlier this year, saying BankAmerica's defensive ''dismembermen t'' of billions of dollars in assets had substantially reduced its value as a takeover target.

The restructuring unveiled by Los Angeles-based First Interstate also features the sale of assets - up to $7 billion worth - as well as restructuring of a variety of businesses.

First Interstate also said it planned to spin off nearly a quarter of its non-performing assets into a new, separate company and to put $2.8 billion in corporate loans into a special unit aimed at getting it out of what it considers non-core lending businesses - including Third World finance.

Harold Meyerman, executive vice president of the company's wholesale bank, said the $2.8 billion consisted of troubled loans to developing countries and good quality, low-liquidity loans to other debtors that are not in geographic and commercial areas the bank considers part of its strategic territory.

The loans will be placed in a special unit with an eye toward getting rid of them, either through loan sales, swaps or simply not renewing credits, as quickly as possible, Meyerman said.

First Interstate also disclosed a unique plan to wipe about $400 million of its $1.7 billion in other non-performing assets, mainly real estate assets, from its balance sheet. It would place those assets into a separate, publicly traded company in which First Interstate stockholders would get all the shares as a dividend sometime in 1988.

The company said it believed that holding those assets as part of First Interstate was depressing its stock price, and clearing them off its balance sheet could enhance shareholder values.

Units to be sold or restructured included the loan operations and government securities trading business of First Interstate Bank Ltd. and parts of its mortgage and leasing units. Most of the job cuts will be through the sale of businesses, while the rest will result from layoffs.

The company also plans to sell a Denver office building and its interest in its Los Angeles headquarters building.

First Interstate took a $95 million third-quarter charge against earnings for costs stemming from the overall restructuring, but said the program should mean annual after-tax gains of at least $75 million.

Chase, which is surpassed only by Citicorp among American banking companies, said it took a $50 million special charge against its third-quarter earnings because of its restructuring.

Chase said the job cuts would bring its total staff reductions since July 1986 to 5,100 employees, or about 10 percent of its work force. Jobs also have been eliminated by the closing of scores of U.S. and foreign offices and branches deemed strategically unimportant or unprofitable.

The company also said it expected to build capital through gains on the sale of undervalued assets over the next year.

Other major banks have taken similar steps recently to raise capital and improve profitability.

Chemical New York Corp. announced a restructuring in September that will eliminate 2,100 jobs and close some offices, and Citicorp said earlier this month it was selling major portions of its landmark Citicorp Center and another Manhattan headquarters to a Japanese company for $670 million.