Throughout his managerial career, Manager Davey Johnson has long been a proponent of rapid improvement while sticking to a player-development model. (Jonathan Newton/WASHINGTON POST)

When your team has been very bad very recently but you think you can be pretty good pretty soon, the final six weeks of a long baseball season can be a tough test of judgment. For the sake of developing key rookies or giving a comeback chance to a veteran, do you risk a late-season collapse?

As the Washington Nationals (58-63) reach the final fourth of their year, they face a delicate, dangerous balancing act that could help their future but might deflate this season. Get ready for lots of Chien-Ming Wang and Ross Detwiler in the rotation, plus slugger Chris Marrero and either Brad Peacock or Tom Milone joining the pitching staff. Even Steve Lombardozzi might arrive along with familiar faces like Roger Bernadina and Yunesky Maya.

As Jordan Zimmermann is shut down by an innings limit, the return of Stephen Strasburg, for as much as five starts, may only be three weeks away.

Like any perennial loser, the Nats feel pressure to show their own players and fans, as well as free agents and stars with no-trade clauses, that they are making true progress.

Going from 59 wins in 2009 to 69 last year to 78 this season (their current pace) would make a convincing case that the franchise is squared away, despite a team president and a manager quitting unexpectedly within the last year. And despite that Jayson Werth contract, too.

Teams are tempted to say one thing in public but actually grind for every win to stay close to the security blanket of .500. If the Nats lose a few, they may be tempted to overwork Tyler Clippard and Drew Storen, keep playing Laynce Nix despite a bad heel or ditch Wang if he stinks back-to-back.

It’s easy to claim you’re developing players while barely helping them. You can bring up Peacock or Milone (40-man roster issues probably preclude both this year) to pitch a few innings in a blowout, yet not allow meaningful innings. You can talk up Marrero’s .310 year at Syracuse but only use him to pinch-hit instead of starting him 10 or more times at first base with Michael Morse moving to left field.

For now, the Nats appear to have set their jaw and decided to play out the season the right way and hope they don’t hit a late-season mega-skid. If you don’t think “how you finish” impacts the future, ask the Orioles. For a decade every light in their tunnel proved to be an onrushing September train.

If the Nats get to .500 this year, or finish ahead of the Marlins and Mets, they’ll do it the hard way: making choices from a long-term perspective, finding out what they hold with Wang and Detwiler, who might end up earning themselves as many as a dozen starts apiece.

That suits Manager Davey Johnson, born contrarian, whose trademark from the Mets to the Orioles to the Reds was rapid improvement while still sticking to a player-development model.

“I’ll be happy when we get to September,” he said this week. “I’ve never liked the way this roster was constructed. My teams always had two long men in the bullpen, like the Phillies have, and bats off the bench.”

The Nats had seven short relievers and gloves on the bench. It drove Johnson nuts.

“All season I asked ’em, ‘Man, how are you doin’ it?’ ” he said. “All the things I was warning them about started happening as soon as I got here.”

An unlimited September roster may actually suit Johnson’s style better.

Scary but fun, here it comes. The flashiest example: Strasburg, who’ll probably get five September starts, just as Zimmermann got seven starts late last season. That sounds great.

But Zimmermann, so excellent this year, was utterly erratic then — brilliant three times (1.06 ERA, 17 strikeouts, one walk) and awful four times (9.64 ERA, 2.357 WHIP). With a year’s rust, Strasburg may be more precise and much better in ’12 than he is next month.

“Stephen is coming back for all the right reasons,” his friend Storen said. “Two things about him that stand out are that he’s really humble — almost naive. Last year, he didn’t understand what a big deal he was. And he’s also really, really competitive. If you could take all the best hitters in the world down to Viera, Fla., he’d never leave. He’d battle them with nobody in the stands and he wouldn’t care.”

If it’s all the same, watching him face them in Nats Park suits me better.

Last September, the Nats brought up Espinosa and Wilson Ramos, both special immediately and now fixtures. This time, the kiddie logjam is bigger. Peacock, the 1,231st pick in the 2006 draft, is now all grown up and touches 97 mph. The Nats compare his stuff and control to Zimmermann.

Milone, a lefty with a Livan-speed fastball but 10-to-1 strikeout-to-walk command, also might deserve a shot at next season’s rotation.

“Milone knows how to pitch. He just gets ’em out,” said Storen, a teammate for part of ’10.

The Morse-sized Marrero needed six bush-league years to improve, well, everything. But after hitting .310 at Class AAA with just five errors at first base, he’s back on the radar. With Adam LaRoche returning next season, the Nats need to see where Marrero fits. So, Morse is oiling his outfielder’s glove.

The warmest story is Wang, who spent two years in Viera rehabbing a shoulder, alone except for his trainer-interpreter and visits from wife and child.

“Try staying in Viera for two years, almost by yourself, not speaking the language all that well,” General Manager Mike Rizzo said.

The normal maximum human dosage of Viera is five weeks for spring training.

So, what was it like? Deadpan, Wang answers slowly, gravely, in English, “There . . . is . . . nothing.”

Then he laughs. Something the Nats hope they’ll still be doing at season’s end.