Bartolo Colon could be the front-runner to start for the Red Sox on Tuesday.

The Journal / Glenn Osmundson

BOSTON –– It’s an article of faith that teams need pitching depth to survive the six-month-long season. The season is just a quarter of the way complete and already the Red Sox have been reminded of that truism several times over.

Last month, for three consecutive days the Sox were forced to adjust their rotation. First, Josh Beckett was scratched because of a stiff neck and David Pauley was summoned from Pawtucket. Next, when Daisuke Matsuzaka fell victim to the flu, Jon Lester pitched on short rest. Finally, with no pitcher for Lester’s original slot, the team was forced to dip down to Double A Portland and promote Justin Masterson — for several hours, anyway.

Now the Sox again face a temporary arms shortage. Clay Buchholz’s stay on the disabled list means the Sox need a starter for Tuesday.

“We kind of have an idea,” said manager Terry Francona last night after the series-opener with Milwaukee was rained out, resulting in a day-night doubleheader today. “I think we know where we want to be.”

But the rainout may have complicated things further.

With a doubleheader today, the Sox face the prospect of running through the bullpen with 18 innings to play in the span of 10 hours.

Further, with Matsuzaka, last night’s starter, now pitching today, his next scheduled turn will come Wednesday.

Thanks to last night’s postponement, Matsuzaka will be going on short rest, meaning the Red Sox may need two pitchers from beyond the current 25-roster before the homestand is completed.

Matsuzaka and Tim Wakefield will pitch today, with Beckett set for tomorrow and Lester slated for the first game against the Kansas City Royals.

Beyond that? Who knows. And threatening weather forecast for both today and tomorrow could either make things worse, or potentially easier.

The options, meanwhile, are many.

Bartolo Colon, who was impressive Thursday in a six-inning, one-hit effort for Pawtucket as part of his rehab stay, would be the most obvious choice.

“The reports on Bartolo were very good,” said Francona. “He pitched very well.”

Still, there were indications yesterday that the Sox were leaning away from that choice.

When Colon is eventually promoted to the big-league roster –– something that almost certainly will take place before the June 1 opt-out date in his contract –– the Sox want him to remain in the rotation.

If the Sox are looking for just one or two starts, that would seem to interrupt Colon’s progress as be rebuilds arm strength following his oblique muscle pull.

Other options include Pauley –– who like Colon pitched well Thursday –– as well as Masterson, despite the fact that the latter has been knocked around in his last few starts at Double A.

What impressed the Sox so much about Masterson’s start against the Angels last month –– during which he allowed a single run in six innings in his major-league debut –– was his poise and maturity.

Making the jump from Double A, Masterson never seemed or felt out of place.

In time, the Sox could shift Masterson to the bullpen for the short term and hope he makes the kind of impact Joba Chamberlain made for the Yankees in the final two months of last season.

But that won’t happen until the second half of the season, after Masterson graduates to Pawtucket and gets some experience pitching in relief.

For now, he may be the Sox’ best option for Tuesday.

Pauley, not effective in his audition last month, is still regarded by the Sox as someone who can contribute at the big-league level.

Though his stuff isn’t as explosive as Masterson’s, Pauley’s sinker-slider combination is effective enough and, through experience, he has come to understand the importance of command and changing speeds.

For a pitcher facing a lineup that will be unfamiliar with him beyond some scouting background, that could be enough.

Charlie Zink has pitched well after de-emphasizing his signature knuckleball, but is not, despite some speculation to the contrary, a candidate.

Either way, before the season is even two months old, the Sox are facing the prospect of a second stretch of back-to-back games during which they must patch and fill from within their system.

That alone should render the suggestion in March by some that signing Colon was a luxury the Sox did not need.

Very soon, it may become obvious that they could use another dependable pitcher like him –– or two.

smcadam@projo.com