Cisco Systems Inc CEO John Chambers warned of unusual uncertainty in the economy and forecast revenue that missed Wall Street targets, sending its shares plummeting and raising fears that a nascent recovery in technology spending could be derailed.

The cautious comments from the man often known as Silicon Valley's biggest cheerleader disappointed investors who had expected growing Internet traffic would spur stronger sales of Cisco's network equipment and send a positive signal to the broader technology sector.

We are seeing a large number of mixed signals in both the market and from our customers' expectations, and we think the words 'unusual uncertainty' are an accurate description of what is occurring, Chambers told analysts on Wednesday.

Shares in the networking giant and industry bellwether dived 8 percent after-hours, weighing on other tech names. Rival Juniper Networks slid 3 percent in extended trading, while International Business Machines Corp was down over 1 percent. EMC Corp fell over 2 percent.

Cisco is expected to depress Wall Street on Thursday, with Standard & Poor's 500 futures down 0.4 percent and Nasdaq futures off 1.2 percent. <.n>

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