Major League Baseball is attempting to institute instant replay on home run calls before the end of this season, according to two sources familiar with those discussions. However, in order to accomplish that, MLB still needs to settle on a replay system that would satisfy everyone involved, from the umpires to commissioner Bud Selig.

USA Today reported Friday on its Web site that MLB had approached the World Umpires Association about implementing replay on Aug. 1. However, it appears that's merely a tentative target date. While it's possible a system could be in place that soon, some baseball officials merely want to get some form of replay system up and running before this year's postseason.

As recently as a few weeks ago, baseball officials were still talking about experimenting with replay during the Arizona Fall League, the World Baseball Classic and spring training before implementing it in the big leagues. But so many people within the sport have reached the conclusion that replay is now inevitable, they're pushing to get it in place as soon as possible.

Their thinking, according to the same sources, is that if there no longer is any serious opposition to the principle of using replay to decide home run calls, it would be embarrassing to the sport to have a big game down the stretch, or in October, decided by a blown home run call. They're hoping to settle on specifics that would be acceptable to Selig, the umpires' union and the players' union.

However, a source told ESPN.com he believes the umpires are in favor of replay as long as it's done in a way that protects and supports them. And while Selig still hasn't given the go-ahead, it's believed he would support a system that would preserve the character of the sport and not delay games significantly.

The idea of replay has gained momentum after umpires botched several home run rulings on national TV in May.

At Yankee Stadium, umpires reversed their correct call and concluded a home run by the Mets' Carlos Delgado was foul.

The following night in Houston, umpires mistakenly ruled a ball off a center-field wall was in play, prompting a reconfiguration at Minute Maid Park the next day.

And, again at Yankee Stadium, a ball hit by Alex Rodriguez that struck a stairway beyond the outfield fence and bounced back into the outfield was ruled a double when it should have been a home run.

Chicago Cubs pitcher Jon Lieber said before Friday's game that he supports the idea of replay.

"The game needs it and I think it does need it soon," Lieber said. "With technology the way it is today, there's no reason why it shouldn't be a part of the game."

Cubs manager Lou Piniella said he doesn't think replay is needed.

"I don't think it's needed at all, to be honest," Piniella said Friday. "How many times do you see players make errors? Baseball has talked about speeding up the game. It's all you hear. All of a sudden, they want instant replay? You're going to have slower games and more restless people in the stands."

Last November, general managers voted 25-5 to try replay on boundary calls. At the time, Selig took the recommendation under advisement.

Selig, like many of the game's traditionalists, has always liked the human element of baseball, and that meant tolerating an occasional wrong call by an umpire. He also worried about further bogging down a sport that has been criticized for its slow pace.

Count Pittsburgh outfielder Jason Michaels in that corner.

"Here's the thing: I guess I'm old-school, but I think human error is part of the game," Michaels said. "It's always been that way. I would think I'd be against it."

In recent years, the new and cozy ballparks, with their quirky dimensions, odd angles and yellow lines that denote home runs, have made it more difficult for umpires.

"If that is what it takes to get the calls right," Pirates outfielder Nate McLouth said. "They [say] it will make the game longer, but it might actually make it faster because won't have all the arguing. But use it just for home runs; the umps are there are a reason. But some home run calls are so close -- we've had a couple this year."

Jayson Stark covers Major League Baseball for ESPN.com. Information from The Associated Press was used in this report.