By Aidan Malley

Published: 05:50 PM EST

A new investment note from JPMorgan reveals confidence that Apple's MacBook line is strong enough overcome dropping notebook sales at its rivals, but cautions that the post-holiday lull may eat into the company's iPhone and iPod numbers.

The financial firm's primary analyst for the report, Mark Moskowitz, refers to sources within the industry who suggest that Apple may be one of the few computer builders to have increased its shipments of portables from quarter to quarter.

While the overall computer market is predicted to drop by 9.2 percent between the quarters ended in December and March, the Mac maker is estimated to have grown its portable shipments by about 0.2 percent in the same three months of 2008. The gain would put Apple's combined MacBook, MacBook Air, and MacBook Pro deliveries for the latest quarter at nearly 1.37 million units.

Apple's desktop sales are expected to dip about 20 percent but is subject primarily to the same seasonal dips as other designers, according to Moskowitz.

iPhone and iPods are likely to be the real concern for investors, he says. JPMorgan is ramping down its estimates for iPhone and iPod shipments from approximately 1.6 million and 10.1 million units each in the March quarter to 1.5 million and 9.7 million units.

Aside from the expected post-holiday drop in sales, the reduced forecast stems partly from anticipation for the launch of a 3G-capable iPhone, which may encourage some prospective buyers to defer their purchases until an expected release later in the year. Moskowitz sees little to fear, as any immediate weakness in sales is likely to be recouped by strength later in 2008.

"As long as there is nothing to suggest that a summer launch of the 3G phone is not a possibility, we would expect investors to look past any near-term disappointment in iPhones," he explains."

For iPods, the analyst is worried only that the iPhone may be cannibalizing their sales. Apple is likely to have higher profit margins on both device types courtesy of steady drops in flash memory prices and recent hard disk drive discounts.

Moskowitz also cautions that even Apple's expected strong MacBook shipments are unlikely to assist the Cupertino, Calif.-based company in evading disappointing results. Although JPMorgan is raising its estimates on Apple's earnings from $1.05 to $1.09 per share, the electronics producer is still seen as falling prey to the same macro-economic factors as its challengers during the spring quarter.

"Across the tech hardware sector, we still believe that the June quarter could be the toughest in five years for investor sentiment, not to mention business fundamentals," the analyst says.

Apple has scheduled its latest quarterly results announcement for April 23rd.