To the highly untrained eye, Sage Rosenfels looks more accurate, more comfortable and more qualified than Tarvaris Jackson to stand next in line behind a 40-year-old quarterback with leaky pass protection that threatens the greatest streak of longevity in sports history.

So rather than ask whether the Vikings should risk exposing rookie Joe Webb to waivers or trade Rosenfels to Buffalo for a sack of footballs in 2012, we might want to ask, "What happens if Brett Favre falls down and doesn't get up for the first time in 20 years?" Or "Why is the second-best quarterback, at least to the untrained eye, the No. 3 guy with no hope of moving up and no guarantee of even making the team?"

To assume the backup quarterback doesn't matter because Brett Favre is the starter isn't being prudent. There is no guarantee that Favre's 309 consecutive starts will grow by 16 to 20 games this year.

If Favre goes down, the development of a sixth-round project won't matter. Rosenfels' contract and trade value won't matter. What will matter is having a veteran leader who can take over a team whose current window of opportunity slams shut the moment this season ends.

I'm not president of the "Sage Rosenfels Fan Club," commander of the "Junk T-Jack Brigade" or lead rider in the "Fire Childress Even Though He Went 12-4 Posse." I also don't consider myself higher than Childress on the QB Guru-o-Meter because I picked Dan Marino for my 1984 fantasy team. So I asked Childress to explain why Jackson is entrenched at No. 2 while those of us in the Dumbell Division don't get it.

"Right from the first day of training camp, I've just seen an evolution in the growth in Tarvaris," Childress said. "Not that I haven't seen it from Sage. He's been the beneficiary of having that extended [playing] time, where he was able to flash.

"We kept the 'ones' [first teamers] in for that one series against St. Louis [in the preseason opener]. I thought Tarvaris played decently in the snaps he got against San Francisco. But really it's the day-to-day thing. You can say, 'Well, yeah, but it's about the games,' but we give them opportunities based on what we see in practice."

Jackson started against the Rams and threw only four passes, completing two. Rosenfels threw 34 passes, completing 23 for 310 yards and three touchdowns. But it's hard to say Rosenfels outplayed Jackson when Jackson really didn't get a chance against a pitiful team.

Against the 49ers, Jackson completed seven of 11 passes for 43 yards. Rosenfels completed two of seven for 11 yards. That was pretty much a wash.

Saturday against Seattle, Jackson played two series and Rosenfels played one. Under Jackson, the offense sputtered to a halt. His first three pass attempts included two short misfires to running back Albert Young and a sack on third down. He went 1-for-4 for 4 yards and lowered his completion percentage to .556.

Under Rosenfels, the offense woke up and won the game. His first three pass attempts were completed for 37 yards and two first downs. He drove the team 87 yards by completing 5 of 6 passes to four different receivers for 71 yards while raising his completion percentage to 63.8. He capped the drive with perfect touch to Javon Walker, who made the 25-yard TD catch over a cornerback in the end zone.

"I'm seeing the field well right now," Rosenfels said. "I'm definitely comfortable in the offense this year as opposed to last year."

The untrained eye also can't envision Webb and Jackson both being the quarterback of the future. If Webb is that good, the Vikings should keep all four quarterbacks and release kickoff specialist Rhys Lloyd. If keeping four quarterbacks isn't an option, they should let poor Tarvaris hop an early flight to somewhere Favre isn't.

Rosenfels is young enough (32) and he's under contract for next year. Jackson has a one-year deal and most likely will leave once he's granted free agency, possibly as early as 2011.

For now, however, the reality, good or bad, is Jackson is entrenched at No. 2 and Rosenfels is No. 3. Asked if anything other than injury could change that pecking order in Thursday's preseason finale against Denver, Childress said, "It probably would be hard for it to change."

Mark Craig • mcraig@startribune.com