Updated from 11:56 a.m. EST

A day after

Aetna

(AET)

rejected a $9.9 billion takeover

offer, William H. Donaldson, its chief executive, said Monday that the company was not seeking a buyer.

But snubbing the joint takeover offer from

Wellpoint Health Networks

(WLP)

and

ING Group

has put Donaldson under mounting pressure from shareholders. In a conference call with analysts Monday, he outlined a few new details of his plan to increase the 147-year-old health and life insurer's lagging stock price.

Aetna's stock fell 5 1/4, or 9.4%, to close at 50 3/4 in heavy trading Monday. The joint takeover offer was valued at $70 a share.

"There were considerations other than the financial considerations that made us not want to be responsive to the Wellpoint/ING offer," Donaldson said.

Aetna, which has also said it will split into separate health care and financial services companies, plans to sell its stake in 35 separate joint ventures in 17 countries. The holdings have a market value of around $4 billion, and a book value around half that amount, Donaldson said.

Analysts said the ventures amount to little more than management headaches. If they accomplish nothing else, the sales may make Aetna easier to value, one analyst said.

Both ING and Wellpoint declined to back down, each saying they still consider the proposed terms favorable to Aetna shareholders.

ING board members are "standing back to see what the shareholders' reaction is going to be," said Amy Fly, spokeswoman for ING. While the stock price movement and Internet message board chatter clearly reflected an unfavorable reaction to Aetna's choice, she said it was too soon for the board to decide what it will do "going forward."

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"Usually, ING does not opt for hostile takeovers," she added.

Wellpoint issued a substantively similar statement Sunday. On Monday, Ken Ferber, a spokesman for Wellpoint, said there would be "absolutely no hostile takeover bid."

Aetna's stock has fallen from a 52-week high of 99 7/8 since the company bought the loss-making health care unit of

Prudential Insurance

for around $1 billion in August. The falling stock price led the company to hire Donaldson, a founder of the

Donaldson Lufkin & Jenrette

securities and banking firm, to replace Richard L. Huber on Feb. 25.

Though it came at a significant premium to the stock's current price, the takeover offer is an albatross for Donaldson. Some analysts, including those who doubt the efficacy of keeping the health care and financial services businesses together, said the company could be worth more than $70 a share if its assets are properly organized and managed.

"There's a lot of people who want $70 today," said Joseph France, analyst for

Credit Suisse First Boston

. "I do believe that $70 is too low. This is one way to smoke out a better valuation." France rates Aetna a buy, and his firm has done no underwriting for the company.

Donaldson denied that in the conference call, though he said the company would consider any offers and has received "indications of interest" for the financial services portion of its business.

"It's not a play to get a better offer," Donaldson said. "Any offer just is not the right way to run a business."

In the conference call, one analyst questioned Donaldson about the company's projected earnings, asking "What could change materially so that it wouldn't be a little over $5?" Analysts polled by

First Call/Thomson Financial

have predicted an average of $4.88 a share for the fiscal year 2000.

"There are a lot of moving parts," Donaldson responded. "There've been no real surprises in our examination. The question is, how can we improve the predictability?"

The company will provide more details after an April 27 company meeting, he said. France, the Credit Suisse analyst, said that without a takeover offer on the table, the company's review of its books could be a mistake, leading Aetna to tip its hand to potential buyers.

Had Aetna announced its plans to burnish the stock price three months ago, "there wouldn't have been an issue," France said. "But because they have this putative $70 offer on the table, people are upset."

Donaldson signaled he was aware of the pressures, ending the conference call by telling analysts that his own compensation is tied to the company's stock price.