Infinera (INFN) shares are sharply lower in later trading after the company provided disappointing Q3 guidance and reduced its growth forecast for 2008.

For Q2, the communications equipment company reiterated previous guidance of revenue of $88 million to $90 million and profits of 1-2 cents a share.

However, for Q3, the company now sees revenue of $75 million to $80 million, well below the Street consensus of $97.7 million. For the full year, the company now sees revenue growth of 10%, down from a previous forecast of 25%.

Infinera said the weak Q3 outlook reflects expectations that North American customers will purchase less product in the quarter than previously anticipated. The company said the shortfall “is related to the timing of new network builds at existing customers and the sales cycle with potential new customer wins, along with a product transition associated with its recently announced new system.”

In after hours trading, INFN is down $3.54, or 25.6%, to $10.27.