Corporate financier Carl C. Icahn yesterday stepped up the pressure on Time Warner chairman and chief executive Richard D. Parsons to take quick action to boost the company's stock price, accusing him of a "dismal record of mistakes," overspending and ignoring the interests of stockholders.

Icahn, who heads a dissident group that owns 2 to 3 percent of the company, wrote in a letter to shareholders that Parsons and his management team wasted $800 million building an opulent new corporate headquarters in Manhattan. He complained that the company is still being steered by most of the directors who oversaw Time Warner's "disastrous" merger with America Online Inc., and said he would hire a consultant to scrutinize the company's spending.

"Time Warner has allowed costs to become bloated due to lack of oversight by the Board and senior management," Icahn wrote. "Nowhere is this more evident than by looking at the Company's landmark headquarters in New York, which . . . offers such lavish features as a grand employee cafeteria with two story windows overlooking Central Park. We question how such an extravagant building, which houses only a small fraction of Time Warner employees, enhances shareholder value (and cannot help but wonder where the shareholders get to eat lunch)."

In a written response, Time Warner said it is pursuing initiatives to increase its stock price, including talks with Microsoft Corp. and others about possible new partnerships involving the Dulles-based AOL subsidiary. Parsons has said Time Warner would be willing to sell a stake in AOL to a partner if that would increase the value of the business. In addition to negotiations with Microsoft, Time Warner has been in talks with Google Inc. and Yahoo Inc. about possible deals involving AOL.

"To the extent that opportunities are now available to enhance value at AOL, which we believe there are, we implore management and the Board to move more decisively than they have in the past," Icahn wrote in his letter.

While saying that he is frustrated with Time Warner's stagnant stock price, Parsons has said his strategy to turn AOL around -- by providing free content, increasing its audience and profiting from ads -- is working, despite a continuing drop in the Internet service's dial-up subscriber base.

Time Warner also said yesterday that it has pursued a sound financial strategy by paying down debt, enabling it to undertake a responsible stock buyback program and increase the footprint of its Time Warner cable subsidiary by agreeing to purchase cable systems from Adelphia Communications Corp. Time Warner plans to spin off part of the cable business to stockholders after the Adelphia acquisition is completed next year. Icahn wants the entire cable business sold.

"The management team has proven its commitment to shareholders and its openness to constructive ideas from knowledgeable people," Time Warner said in a written statement. "We look forward to sharing our next steps with our shareholders in the coming weeks."

After meeting with Parsons and praising him earlier this year, Icahn's letter marks a turning point in his attack on the company and its leadership. Icahn is seeking an immediate $20 billion stock buyback program. Time Warner has proposed a smaller repurchase plan.

Icahn questioned whether the board of directors is detached enough from the ill-fated merger with America Online, which wiped out tens of billions of dollars of shareholder value. He pointed out that seven of the 11 Time Warner directors who approved that deal are still on the board.

"The lingering presence of these individuals forces us to ask, why are a majority of the same directors who signed off on the disastrous AOL merger still steering the corporate ship?" Icahn wrote.

Icahn has a record of shaking up public companies by buying their stock or bonds, winning representation on their boards and lobbying hard for radical changes. Thus far, his presence as a Time Warner shareholder and critic has done nothing to increase the company's stock price, which closed yesterday at $17.80, down 21 cents.

In addition to AOL and the cable subsidiary, Time Warner owns movie studios, the nation's biggest magazine group and other valuable media properties including the HBO, TBS and CNN cable channels. In dissecting Parsons's performance, Icahn cited asset sales for prices he said were too low, including sales of the Warner Music Group and a 50 percent stake in the Comedy Central cable channel.

"Time Warner owns the most valuable collection of media properties in the industry," Icahn said. "We think that there is a clear distinction to be made between the value of these assets and the creative skill of the day-to-day operators. . . . In the coming months, we will be continuing to speak out about our belief in the need for a new voice for shareholders on the Board of Time Warner."

Carl C. Icahn wants Time Warner to undertake a $20 billion stock buyback program.