NEW YORK (CNN/Money) - Shares of Ford Motor fell on Monday as Wall Street firm Prudential Securities cut its rating on the automaker to "sell" from "hold."

Brokerage house Salomon Smith Barney also lowered its price target on cable television services provider Adelphia Communications, citing concerns about off-balance sheet liabilities. Salomon set a 12-month target of $30 on the stock, down from its previous guidance of $37.

Sun Microsystems stock, however, climbed after Merrill Lynch analyst Steven Milunovich said the network computing giant would likely report higher revenue in its quarter ended March 31 as sales of some products hold up.

Adelphia Communications (ADLAC: down $1.78 to $13.12, Research, Estimates). The telecommunications firm, which last week disclosed that it has $2.3 billion of off-balance-sheet debt in closely held partnerships, also said it is considering plans to sell assets, according to a Wall Street Journal report. The company also asked the Securities and Exchange Commission for extra time to file its annual report.

Ford Motor (F: down $0.76 to $15.73, Research, Estimates). Prudential Securities downgraded the automaker to "sell" from "hold" and lowered its stock price target to $12 from $16. The firm also cut its earnings estimates for 2002 to 18 cents a share from 43 cents and for 2003 to 87 cents a share from $1.

Sierra Pacific Resources (SPF: down $0.45 to $27.65, Research, Estimates). A unit of the company has been denied the ability to recover $437 million of deferred energy costs incurred last year during the California energy crisis. On Sunday, Nevada Power Co., a Sierra Pacific subsidiary, said the Nevada Public Utilities Commission had refused to allow it to recover. A downgrade from Merrill Lynch followed.

4Kids Entertainment (KDE: down $1.87 to $18.05, Research, Estimates). The company, which licenses Pokemon and other kids' entertainment, said fiscal fourth-quarter and full-year sales and profits tumbled.

Wal-Mart (WMT: down $1.74 to $59.56, Research, Estimates). UBS Warburg downgraded the world's biggest retailer to "buy" from "strong buy."

BAM Entertainment (BFUN: down $1.61 to $3.09, Research, Estimates). The maker of entertainment software said sales in the first quarter could come in as low as $6.5 million, versus expectations for as much as $20 million, blaming "delays in scheduled product releases and poor execution of worldwide sales and distribution strategies."

Digital River (DRIV: down $7.71 to $7.10, Research, Estimates). The provider of e-commerce software and services lowered its earnings expectations Friday for the first quarter and the year, citing a drop in spending by information technology companies and lower sales of software products. Deutsche Banc Alex. Brown downgraded the stock to "buy" from "strong buy."

nVidia (NVDA: down $0.73 to $43.63, Research, Estimates). An article in Barron's suggests that the chipmaker could face an increased threat to its market share from competitors Intel, ATI Tech and Creative Labs as PC sales growth remain sluggish.

Stellent (STEL: down $1.25 to $8.38, Research, Estimates). The provider of enterprise content management solutions warned about its fourth quarter, saying it expect revenue to be in the range of $14 million-to-$15 million, citing a slowdown in IT spending by its customers and economic weakness. Analysts had forecast revenue for the quarter at $27 million, according to First Call.

America West Airlines (AWA: down $0.21 to $5.39, Research, Estimates). The carrier said in its annual report it remains doubtful about a major recovery in air travel, predicting that its near-term revenue will continue to be hurt by a soft economy and a decline in business traffic.

RSA Security (RSAS: down $1.71 to $7.29, Research, Estimates). The e-security company warned about its first quarter, saying it expects a loss of between 8 cents and 11 cents a share on revenue of $55 million-to-$56 million. Analysts had forecast a profit of 3 cents a share on revenue of $64.4 million.

Sun Microsystems (SUNW: up $0.70 to $9.52, Research, Estimates). Shares of the network gear maker rose after Merrill Lynch said Sun would likely report higher revenue in its quarter ended March 31 as sales of some products hold up.

Juniper Networks (JNPR: up $0.61 to $13.23, Research, Estimates), Ciena (CIEN: up $0.37 to $9.37, Research, Estimates). Banc of America upgraded the communications equipment makers to "strong buy" from "buy." "We believe this quarter marks a cyclical inflection," the brokerage firm said. "And although we expect only marginal improvement over the next few quarters, we do think the worst has past."

SONICblue (SBLU: up $0.56 to $3.08, Research, Estimates). The company, which makes entertainment technology, said sales for the first quarter are ahead of consensus expectations for $58 million.

PMC-Sierra (PMCS: up $1.37 to $17.65, Research, Estimates). Banc of America upgraded the provider of high-speed broadband communications semiconductors to "buy" from "market perform."

ONI Systems (ONIS: up $0.37 to $6.54, Research, Estimates). Banc of America Securities upgraded the company, which develops, markets and sells optical communications networking equipment, to "strong buy" from "buy."  

--from staff and wire reports