Major League Baseball has signed an agreement with the World Umpires Association, approving the implementation of instant replay for disputed home run calls sometime before the end of the season, one of MLB's top officials told MLB.com on Wednesday.

"We're not there yet," said Rich Levin, MLB's senior vice president of public relations, "but this is another significant step."

All 30 Major League ballparks are being wired with monitors so umpires on location can view replays of questionable home run calls -- fair or foul, in the park or out. Many of the installations are done, but there are still some in the process of being completed. For example, a crew was at Angel Stadium in Anaheim on Wednesday, installing the necessary equipment.

Commissioner Bud Selig said last Thursday at the conclusion of the quarterly owners' meetings in Washington that he was confident all glitches could be ironed out so that the system would be put into place before the playoffs.

"I'm quite satisfied that we're trying to get all the bugs out of it," he said. "It'll be very limited in its form, as you know. I'm a little reluctant to speak out about it until I know everything is working, but we are moving in the right direction."

Resolution of the matter with the umpires came amidst a report on Tuesday that their union was asking MLB to take another look at the project before they signed off.

"A lot of the procedural issues necessary for instant replay to be implemented need to be worked out," World Umpires Association spokesman Lamell McMorris told The Associated Press. "Major League Baseball needs to step up to the plate and iron out these issues."

Umpires were reportedly concerned that, in some places, monitors are being installed too far away from the field and that replay officials at a central location in New York City might be involved in the decision-making process, The AP said. But those issues are now resolved.

Monitors are being placed in different locations at various stadiums -- near umpire dressing rooms in some and in dugouts in others.

The plan is to have umpires at the particular ballpark sent an instant replay feed of the disputed call from MLB Advanced Media's office in Manhattan. The crew chief on site would then be charged with making the decision whether to overturn or sustain the call.

MLB's general managers voted 25-5 this past November at their annual meeting to explore the use of instant replay on a limited basis.

They also were in favor of a central replay location to review disputed home run calls, much like the National Hockey League utilizes in Toronto to review contested goals.

"Yogi once said that it ain't over till it's over so I want to be very careful," Selig said last week. "When we do it I want to make sure it's very good, that it's perfect. We have spent a lot of time, doing a lot of checking. They're wiring 30 parks. And Chelsea, where the headquarters will be at MLBAM, I've been over there to look at it and it's unbelievable.

"It's a lot of fun. But there's still work to be done and I don't want to put a date on it. Let's just say my confidence is growing."