Marriott Corp.'s stock plunged to its lowest point in eight years yesterday amid continuing concerns that tight credit and the slumping real estate market are hitting the Bethesda-based hotel giant with a one-two punch.

One analyst with a major Wall Street firm, Caroline Levy of Shearson Lehman Brothers Inc., was sharply negative about Marriott's prospects, warning her clients that falling property values could force Marriott to take write-offs that would essentially wipe out its net worth.

The report helped fuel a sell-off in Marriott stock yesterday. Its shares lost a whopping 12 percent of their value, falling $1.50 per share to close at $10.87 1/2. About 981,000 shares changed hands, almost three times the company's usual volume.

Marriott's stock has been sliding gradually for more than a year, but the decline has picked up speed in recent months. Since July 20, the shares have lost fully half their market value; since Jan. 1, about two-thirds of their market value have been wiped out.

A Marriott spokesman yesterday reiterated the company's policy of not commenting on its stock activity.

Marriott was among a number of locally based companies that came under selling pressure yesterday as the Dow Jones average lost 59.41 points, or 2.3 percent. Riggs National Corp., parent of the banking company, lost $1.25 to close at $13.50, off 8.5 percent; Computer Data Systems Inc. of Rockville dropped $0.62 1/2 to close at $7.75, off 7.5 percent; and First Virginia Banks Inc. lost 7 percent, closing at $19.25, off $1.50.

While Shearson's Levy was bearish about the prospects for Marriott, other analysts had a less discouraging, if not entirely optimistic, outlook about the largest company in the Washington area. "The real estate market is not in good shape and Marriott has a lot of debt, but there seems to be a lot of exaggeration and over-reaction about {Marriott} in the {stock} market these days," said Joseph Doyle, who follows Marriott for Smith Barney Upham & Co.

Other analysts said that some of the deterioration in Marriott's stock can be traced to the troubles of New Jersey-based Prime Motor Inns Inc., which last week filed for reorganization under federal bankruptcy laws.

Although Prime is an indirect competitor of Marriott's, hotel companies are under pressure because of a nationwide glut of rooms, heavy debt loads and the credit crunch, which makes it difficult to finance new hotels or sell existing ones. Moreover, the threat of a recession makes it likely that discretionary travel will be cut.

Marriott is being watched closely because a large portion of its profits come from developing hotels and selling them to groups of investors. Marriott has about $1 billion of newly constructed real estate on its books and is in the midst of completing another $1 billion or so, according to Doyle.

Levy, in her report yesterday, said Marriott might be faced with writing down the value of some of this property in particularly weak markets.