NEW YORK (AP) _ Aetna Life and Casualty Co. on Friday announced a restructuring plan, including layoffs, to tighten operations and save hundreds of millions of dollars.

The Hartford-based insurance company also announced a 51 percent drop in third-quarter earnings that included a one-time, $60 million charge for severance benefits and other costs associated with the reorganization.

Analysts said the restructuring may be good medicine not only to Aetna but the ailing insurance industry, which has been suffering from soft premiums and poor returns in its real estate and bond investments.

Aetna's announcement ''might set the tone for the insurance industry in general,'' said Denise A. Petsis, an analyst with Argus Research Corp. ''The insurance industry is in a down cycle. ... There's very little room right now to improve revenue, so what they're trying to do is hold the line on costs.

''When the insurance industry rebounds, I think a lot of these companies, Aetna included, will be in a much better position,'' Petsis said.

Aetna, one of the nation's top five insurance companies, said it would save up to $95 million a year by reorganizing its three domestic insurance divisions into two groups. In the process, 2,600 jobs will be eliminated through layoffs and attrition.

''Our goal is to build on the many areas of excellence Aetna must retain, and to solidify our position as a leader in insurance, related financial services and managed health care,'' said James T. Lynn, Aetna chairman.

Aetna's competitors are also retrenching. Travelers Corp., also based in Hartford, recently cut its dividend to save $100 million and said it will become choosier about where it sells coverage. Philadelphia-based Cigna Corp. is consolidating its domestic property and casualty operations to pull in any loose ends.

The '90s will be the era ''where focus will count,'' said Michael Frinquelli, an insurance analyst with Salomon Bros.

''I don't think we will necessarily wind up a decade from now with fewer companies in the business. We will end up with same number - smaller and more focused,'' he said.

Aetna said it earned $88.6 million, or 80 cents per share, in the three months ended Sept. 30 compared to earnings of $183 million, or $1.63 per share, a year earlier.

Revenue slipped 1.2 percent to $4.84 billion in the quarter from $4.90 billion for the same period last year. Premiums rose slightly, to $3.3 billion from $3.2 billion last year.

Under the reorganization, to be put in place March 4, two new groups will be created. One will include managed health care, group insurance, small business employee benefits markets, pension and financial services, individual annuity and pension and sponsored sales.

The other will be made up of commercial markets, national commercial accounts, bond, personal auto, homeowners and individual life insurance.

''All our existing businesses remain, it's just a matter of how they will be grouped and how they will be funded,'' said company spokesman John C. Hawkins.

Aetna said most of the job eliminations would come from its three offices in the Hartford area. About 17,400 of its 45,200 employees work in Hartford, Middletown and Windsor, Conn.

He said it was too early to tell how many of the jobs would be lost through layoffs.

The third-quarter earnings also include net capital losses of $38 million because of additions to reserves and write-downs related to the company's mortgage loan and real estate porfolios.

For the first nine months of 1990, Aetna reported net income of $472.2 million, or $4.23 per share, down 10.3 percent from $525.8 million, or $4.67 per share, a year earlier.

Nine-month revenue slipped 0.6 percent to $14.43 billion from $14.51 billion in 1989. Premiums fell slightly to $9.66 billion from $9.7 billion.