Debt-ridden Baldwin-United Corp. lost $617 million in the first quarter, the company announced yesterday.

Victor H. Palmieri, chairman and chief executive officer of the financial services firm, said the loss includes special write-offs and charges of $567 million. The write-offs were deemed necessary largely because of "doubtful future recoverability of deferred costs and other intangible assets," Palmieri said.

For the 1982 first quarter, Baldwin-United reported earnings of $18 million (90 cents a share).

Baldwin-United's financial troubles have been attributed to the company's $1.1 billion acquisition last year of MGIC Investment Corp. under the company's former chairman, Morley P. Thompson.

Meanwhile, Aetna Life & Casualty Co. says that it has ended a fight with the Securities and Exchange Commission by restating its 1982 financial statements to eliminate $203 million in tax benefits.

The restatement lowered Aetna's operating earnings for 1982 from $522 million ($5.80 a share) to $319 million ($3.50 a share).

Because of the settlement announced Thursday, the SEC has terminated its investigation of Aetna.

Aetna is the largest stockholder-owned insurance and financial services company in the United States.

Five months ago, it refused to restate all of its 1982 earnings, defending its accounting procedure that included future tax credits from property-casualty underwriting losses in current earnings.

The SEC said that Aetna's procedure did not meet the stringent accounting test of assurance beyond any reasonable doubt.