The Mac was one of the few products that failed to live up to expectations in the June quarter (Apple’s fiscal Q3). Analysts were looking for sales of 4.2 million. What Apple (AAPL) delivered was 3.95 million.

That’s not likely to happen again on Tuesday, when Apple reports its earnings for fiscal Q4.

Everybody seems to agree that in a PC market that would otherwise be shrinking, the Mac is one of the few computer lines keeping it afloat, especially after the July refresh of two of Apple’s most popular models: the MacBook Air and the Mac mini.

Of 53 analysts polled in advance of our quarterly earnings smackdown, all but two — Sterne Agee’s Shaw Wu and Janney’s Bill Choi — are calling for Apple to beat the record 4.134 million Macs sold in the holiday quarter last year. Although the estimates range from Wu and Choi’s low of 4.1 million to a high of 5.35 million (from Navin Nagrani of AAPL Independent Analysts), the spread between the institutional and independent analysts is relatively narrow, at least compared with their estimates for revenue, EPS, iPhones and iPads.

The average Mac unit sales estimate among the pros is 4.3 million; among the bloggers it’s 4.7 million. The average estimate of all 53 analysts is a little over 4.5 million, representing 16% growth from the same quarter last year. The Street is looking for 14%, the indies for 21%.

We’ll find out who was closest to the mark next Tuesday at about 4:30 p.m. EST, when the quarterly results hit the business wires. Apple is scheduled to discuss those results in a 5 p.m. conference call with analysts that the company will webcast here.

Below: The estimates we’ve gathered so far and the dates they were submitted, with the independents in green and the institutionals in blue. The rank numbers show how accurate each analyst’s revenue and EPS estimates were over the past three quarters (the lower the better).