Investors in Six Flags Inc. have discovered that two entrepreneurs have plans for turning around the amusement park company, whose stock price has plunged as fast as its roller coasters.

Daniel Snyder, the principal owner of the Washington Redskins, and Bill Gates, the founder and chairman of Microsoft Corp., have bought up big chunks of the 40-year-old purveyor of water parks, drive-through safaris and corndogs.

In a filing yesterday with the Securities and Exchange Commission, Gates said he may seek a spot on the company's board. Snyder made a similar filing Monday. In the documents, both men sharply criticized Six Flags' management.

Gates, who started buying shares in 2002, owns 11.5 percent of the company, or about $54 million worth of stock. Snyder, who started buying the stock in August, holds 8.76 percent, or about $41 million in stock.

Their stock purchases come as Six Flags, which operates 31 theme parks, including one in Largo, struggles with falling attendance and revenue. The company posted a loss of $61.7 million in 2003. In July, it reported a 4.1 percent drop in attendance from a year ago. The company has warned it will miss full-year 2004 sales projections. Its share price has dropped from $8.29 in March to as low as $3.49 on Aug. 10.

The theme-park industry is in a downturn. Attendance fell from 324 million in 2002 to 322 million in 2003, according to the International Association of Amusement Parks and Attractions, which blamed a cold, wet summer. But Six Flags' performance has lagged some of its competitors, according to analysts.

Gates's Cascade Investment LLC said in SEC filings that it is "increasingly dissatisfied" with Six Flags' financial performance. Snyder's Red Zone LLC faulted it for being "continuously outperformed by its peers."

Debbie Nauser, a spokesman for Six Flags, declined to comment.

Gates and Snyder declined to comment on their investment tactics. But two people familiar with their plans said there is no coordination.

"There are similar frustrations but that's it," said an executive at Cascade Investments who has been briefed on Gates's investment strategy but was not authorized to speak publicly on the matter.

Those people said Gates and Snyder independently view Six Flags as a poorly run business that will remain undervalued until there is a change in management strategy.

"Dan thinks there are a lot of things the current management can do that are fairly obvious," said a close associate, who spoke on condition of anonymity because Snyder is still developing his strategy.

Investors appeared pleased with the company's new high-powered shareholders. The stock price rose $1.11, or 25 percent, to close at $5.57 a share yesterday.

Analysts expressed surprise at the two-pronged investor attack on Six Flags management but said it appeared to capture shareholder frustration with the company's performance.

"After a number of poor seasons of operating results, I think large shareholders feel some change is needed," said Glen R. Reid, an analyst at Bear Stearns & Co., the New York brokerage house.

"They've definitely underperformed," said Kit Spring, an analyst at brokerage Stifel Nicolaus & Co.

Analysts blamed the company's debt, which now tops $2 billion, forcing the company to cut back on the number of new rides. "In order to maintain high attendance rates, you have to spend money," Reid said.

Industry observers said Snyder's investment in Six Flags is in keeping with his appetite for trying to turn around undervalued entertainment venues. Snyder, who bought the Redskins in 1999, has turned the money-losing franchise into one of the most financially successful teams in the National Football League.

A person familiar with his plans said Snyder will encourage Six Flags' executives to invest heavily in consumer marketing and corporate sponsorship, just as he has done with the Redskins. That could mean, for example, throwing the Six Flags name on several well-known food and beverage products, that person said.

"Dan understands marketing," said Robert L. Johnson, chief executive of Black Entertainment Television Inc. and owner of the Charlotte Bobcats basketball team. "If there is an asset that is under-marketed and he thinks he can do it better, there is gold in them there hills for him."

In recent times, Six Flags has tried more aggressive marketing. Six months ago, the company launched its first national advertising campaign in seven years. The commercials, which began running in March, feature a tuxedo-clad old man inviting families to escape hectic suburban lives by driving to the nearest Six Flags.

In his SEC filing, Snyder said he may purchase additional stock of Six Flags and may consult with other shareholders about the future of the company. A person who has spoken with Snyder about the matter said he could seek to oust Six Flags' management by rounding up support from a majority of shareholders.

"He thinks the company is poorly run at the top," this person said.

Microsoft Chairman Bill Gates, left, and Redskins owner Daniel Snyder have recently bought substantial stakes in Six Flags, according to SEC filings.Superman: Ride of Steel is one of the roller coasters at Six Flags America in Largo. Debt has kept the amusement park firm from opening many new rides.