How quickly opinions can change. Just last week, I wrote a column lambasting the idea of the Yankees trading for Phillies right fielder Bobby Abreu on two grounds.The first and less important was that Abreu is in decline; the second and more important was that the Yankees cannot afford an indefinite amount of commitments to expensive star players who don’t produce at the level for which they’re being paid.

Now that the Yankees have made the trade, though, it looks brilliant to me. What changed my mind? Money.

Before this trade was made, the consensus was that Abreu would use the leverage afforded him by his no-trade clause to, at the least, demand that a $16 million option for the 2008 season be picked up. It seemed likely that he would also demand a rich extension for seasons beyond.This is the same dynamic we saw play out in the Randy Johnson negotiations two years ago, and there’s nothing in the least wrong with it; just as teams use the leverage they have over players, so do players use the leverage they have over teams.

Even the notion of picking up that 2008 option looked pretty sketchy. Abreu is a liability in the field and is rapidly losing his home run power and ability to hit for average. He’s still a very good all-around player, but his profile is that of one losing his athleticism and bat speed, quickly. He’s not a good bet to be worth anything like $16 million two years from now.

As things went, though, the Yankees are only committed to pay him for the remainder of this year and $15 million for next year; the Phillies apparently paid Abreu $1.5 million to waive any further claims. Suddenly, this is a great trade. A team with the Yankees’ resources should always prefer to pay more upfront in exchange for less long-term commitment. There’s nothing at all stopping the team from signing Abreu past next year should he prove a good fit, but now they won’t have to cross their fingers and hope he isn’t headed toward becoming a Kevin Brown-scale drag on the payroll. It’s a masterstroke, giving the Bombers all the benefits of having a fine player and none of the drawbacks.

Still better: In exchange for taking on Abreu and pitcher Cory Lidle, the Yanks gave up the equivalent of whatever was in Joe Torre’s pockets.Twentyyear-old shortstop C.J. Henry is in low-A ball, has yet to hit .250, and will probably end up a second baseman; he’s not a premium prospect.

Lefty reliever Matt Smith, 27, made a good show in pitching 12 scoreless innings of relief in the Bronx this year, but

made it above Double-A only last year; he’s not a hot commodity. And the Gulf Coast League battery of 19-year-old catcher Jesus Sanchez and 20-year-old starter Carlos Monasterios isn’t much — neither rated among the Yankees’ 20 best prospects coming into the season, and it’s a very shallow system. They have the same chance of coming back to haunt the Yankees as any random prospects not yet of drinking age do, and that chance is a fair price to pay for Abreu and Lidle.

All this being so, the real question right now is how much difference these two players are going to make on the field in an extraordinarily tight playoff race in which four quality teams — the Yankees, Red Sox, White Sox, and Twins — are vying for two playoff spots. It will be an enormous impact. The difference between Abreu and Melky Cabrera or Bernie Williams is, over the course of two months, somewhere around two wins; the difference between Lidle and Sidney Ponson is probably around one win.

That doesn’t sound like much, but it’s exceptionally difficult for any but the very best players to make much more of a difference over such a short period of time. Realistically, it’s the best the Yankees could do, and it’s very good. Those three wins are of tremendous importance to the Yankees right now, and could quite easily be the margin between going to the playoffs and staying home.

That three-wins figure comes from an accounting perspective. Abreu and Lidle will perhaps offer more than that. Abreu’s contributions are heavily concentrated in his on-base average. He’s the kind of player who works pitchers, wearing them out and keeping the lineup turning over. Lidle is no stud, but he’s a consistently decent pitcher who eats innings, and a team with four of those and an inconsistent guy like Jaret Wright at the back of the rotation is very different than one with three of them, Wright, and the awful Sidney Ponson.

It makes a difference to the bullpen, and it makes a difference to the team’s chances of sustaining a long winning streak. Picking up Lidle is big. This is a great trade. We’ll see what the Red Sox do by tonight’s trading deadline, but right now the Yankees are the favorites in the AL East.

tmarchman@nysun.com