The Vikings panicked after starting 0-2, benching quarterback Tarvaris Jackson, 25 and in his third season, in favor of Gus Frerotte, 37 and in his 15th season.

On the surface, this move appears to have been a success. The Vikings are 3-1 with Frerotte and should improve that record against the injury-ravaged Bears defense on Sunday in Chicago.

So, hallelujah to Gus -- except when you have watched the Vikings' offense for the past month, there has been a nagging thought that this team is easier to defend than it was with Jackson.

The reason: mobility.

Frerotte is a standing target. He has made the offensive line look worse than it actually is.

Pass rushers can envision where Frerotte will set up and head hell-bent to that spot. An end or a blitzer closing on Jackson was required to be slightly cautious, or the quarterback could step inside the rush and take off for a first down.

Frerotte does have an understandable advantage in reading defenses over Jackson, and he's more consistent with his throws.

Frerotte also makes his share of mistakes. Three throws in Sunday's 12-10 victory over Detroit -- including an interception -- would have drawn large boos inside the Metrodome if the passer had been Jackson.

Frerotte is 78-for-140 (55.7 percent) for 968 yards. He has three touchdowns and three interceptions. The mediocre numbers do not take into account two other factors that can be traced to Frerotte's inability to make plays on the move:

He has been sacked 11 times for 66 yards, and the Vikings are 19-for-56 on third downs with Frerotte. By contrast:

The Vikings were 7-for-16 on third downs in the opening 24-19 loss at Green Bay. Four of those conversions came on runs by Jackson. He also was 2-for-2 on fourth downs.

Jackson's numbers a week later in the 18-15 loss to Indianapolis were horrendous. He threw for 130 yards -- and the Vikings were 2-for-13 on third downs.

He played poorly, and the numbers were turned more negative by the conservative manner in which the Vikings played the second half.

They were trying to nurse field goals to victory over Indianapolis -- and if Ryan Longwell had made his sixth from 48 yards, the Vikings would have been 1-1 and Jackson would've remained at quarterback.

The passing yardage has increased with Frerotte. The average is 247 yards through the four starts, including a season-high 296 last Sunday.

The number was inflated when Bernard Berrian turned an 8-yard throw into an 86-yard touchdown on a play designed for him as the primary receiver. It was an easy throw for Frerotte, as it would have been for Jackson, or Spergon Wynn.

Vikings followers filled their pauses in lambasting coach Brad Childress this week by complaining about the work of the offensive line.

Clearly, Ryan Cook was a swinging gate at right tackle, but much more perfection is required from the blockers with Frerotte at quarterback. The 11 sacks in four games would be a half-dozen with Jackson -- and the third-down conversion rate would be better with his scrambles past the sticks.

One theory on the switch to Frerotte was that a more dangerous passing game would prevent opposing defenses from loading up to slow Adrian Peterson.

Another theory bites the turf.

There's no need to account for a run by the quarterback with Frerotte, and more defenders than ever are now present to smother Peterson.

He had 48 carries for 263 yards (5.5 per carry) in Jackson's two starts. He's 81 for 300 yards (3.7) with Frerotte.

If I'm a defensive coordinator and the Vikings are third-and-7, I like my chances of a stop knowing the only option is Frerotte throwing for it, rather than Jackson throwing, breaking from the pocket or rolling out.

The Frerotte enthusiasts -- or "Gussies," as they are known in Vikingsland -- point to a 3-1 record as proof the switch to the vet was fortuitous.

If that's all that matters, then Jackson's 8-4 record as a starter in 2007 should have built up enough credit to get him more than two starts to open a new season.

Either way, we'll discover in the next few weeks if the Vikings are better off with Frerotte or Jackson, since Stand-Tall Gus is going to get hurt and the kid will get some starts down the stretch.

Patrick Reusse can be heard weekdays on AM-1500 KSTP at 6:45 and 7:45 a.m. and 4:40 p.m. preusse@startribune.com