BOSTON — A terrific start, followed by a long stretch of mediocrity.

Is this starting to look at all familiar?

If you’re a Red Sox fan, the answer, of course, is yes. The only thing still to be determined is whether this season is a replay of 2002 or 2004.

Both times, the Sox broke well from the gate. Both times, they stumbled in midseason and played sub-.500 ball for an extended period.

In 2002, they never recovered, finishing out of the postseason despite a 40-17 record on June 6. In 2004, the Sox righted the ship and went on to capture their first World Series in 86 seasons.

Which form will be followed in 2007? The next month or so may provide the answer.

To be sure, such struggles are hardly unprecedented for successful teams. In fact, each of the last four world champions — the 2006 St. Louis Cardinals, 2005 Chicago White Sox, 2004 Red Sox and 2003 Florida Marlins — all suffered through portions of their respective seasons in which they lost more than they won for 40 or more games. Blame parity, the ever-increasing role of injuries and poor depth for those exaggerated slumps.

In that respect, these Red Sox are already showing championship form, having gone 20-23 in their last 43 games, slightly more than one-quarter of the schedule.

One thing, however, is sure: The Red Sox aren’t about to save their season with a deadline deal, as they did in 2004.

Remember that general manager Theo Epstein labeled the team’s poor defense its “potentially fatal flaw,” leading him to pull off a complicated four-team swap that overhauled the team’s infield with a new shortstop (Orlando Cabrera) and first baseman (Doug Mientkiewicz).

Complicated as it was, things fell together nicely for the Sox. Nomar Garciaparra, who was the infield’s weakest defensive link, still had value on the trade market despite being in the final year of his contract.

The improved defense allowed the team’s pitchers to be more aggressive, confident that the plays would be made behind them. After a two-week period of adjustment, the Sox took off in the middle of August and never looked back until they were parading around Busch Stadium with the trophy.

They probably won’t be so lucky this time.

For one thing, big deadline deals seem to be a thing of the past. The last two seasons have seen lots of talk and little action. Teams zealously guard their best prospects, refusing to surrender them for short-term help and quick-fix solutions.

Salary dumps, too, are now nonexistent, as baseball’s revenue sharing program has eliminated the need to sell off expensive contracts.

Even if the Sox could pull off a big trade, it wouldn’t necessarily cure what ails them.

“There’s nothing out there to fix what’s wrong,” said one baseball executive of the Red Sox’ current plight.

Defense isn’t the issue this time. The problem is an underperforming lineup which, at its current pace, would barely manage to score 800 (808, to be exact), much less the 900 runs the team tallied in each season from 2003 through 2005.

The Sox aren’t about to land a cleanup hitter to replace Manny Ramirez or upgrade their No. 3 hitter by getting someone better than David Ortiz. They need Ramirez and Ortiz to snap to life in the middle of the lineup and begin their tandem assault on American League pitchers like they did the previous three seasons.

As a team, the Sox need to greatly improve their success with men in scoring position. Going into last night, they were a woeful .238 in those situations since June 1, neatly coinciding with their current funk.

Expensive free-agent acquisition J.D. Drew may be hitting .323 over his last 19 games, but he’s been a colossal bust as a run producer, as evidenced by his paltry .385 slugging percentage.

Can the Sox rediscover their mojo in time? Of course — 68 games still remain. But this time, they’ll have to do it on their own, with little outside help.

If they find themselves and peak in October, they can extend the streak of world champions who overcame a month or so of lethargy to five.

smcadam@projo.com