By Katie Marsal

Published: 11:00 AM EST

Shares of electronics maker Apple Inc. rose sharply in early morning trading on the Nasdaq stock market after an analyst for CitiGroup said the company is likely to beat current quarter Mac sales estimates and continue to see a rise in gross margin.

"Supply chain checks and NPD data suggest meaningful upside to consensus PC unit estimates for Apple in [its fiscal fourth quarter of 2007]," analyst Rich Gardner wrote in a report to clients. "We are raising our September quarter PC unit estimate from 2.0 million to 2.17 million units on stronger than expected iMac momentum following the August 7 product refresh."

Following highly publicized reductions in the iPhone build plan one month ago, the analyst also said he now believes that build plans for the handset have been reduced to "very attainable levels" in the 3.8 million to 4.0 million unit range for calendar year 2007.

"We expect the next revision to iPhone build plan to be an upward revision, especially given the September 5 price reduction from $599 to $399," he wrote. "It has been our view for some time that a significant price reduction would be necessary in order to make iPhone a truly high volume product. Our checks suggest that consumer response to the price cut has been swift and meaningful."

Meanwhile, Gardner raised his fiscal 2008 and fiscal 2009 earnings-per-share estimates on Apple to reflect higher gross margin and lower operating expense assumptions without changing revenue estimates significantly, which remain near consensus estimates.

"Our gross margin revisions reflect our belief that gross margin is likely to continue its upward progression in fiscal 2008 and fiscal 2009 due to above-corporate average margins on iPhone service residuals and accessories," the analyst wrote. "Fiscal year 2008 gross margin should also benefit from the Mac OS Leopard upgrade cycle."

Gardner, who reiterated his Buy rating on shares of the Cupertino-based company, also raised his 12-month price target to $185 from $160. Shares of Apple were trading up 3.5 percent (or over $5) to $149.20.