New York Mets right fielder Carlos Beltran may be the prize as baseball nears Sunday’s trade deadline. (Francis Specker/AP)

Fundamentally, very little distinguishes the Philadelphia Phillies, San Francisco Giants and Atlanta Braves from each other. The three best teams in the National League, each enjoys a cushion of at least 4½ games in the hunt for playoff spots. Each is built around starting pitching — ranking first, second and fourth, respectively, in the league in starters’ ERA. Seven of the nine starting pitchers on the NL roster in the All-Star Game two weeks ago came from those three formidable staffs.

But each contender has a flaw, and it is basically the same flaw: They all sometimes struggle to score runs, and find themselves, about two months from the end of the season, in need of a hitter. All have an opening in the outfield — entering Monday, the Phillies, Giants and Braves ranked 12th, 13th and 15th in the NL, respectively, in combined OPS by outfielders.

By the end of this week — by 4 p.m. Sunday, to be exact — one of these three contenders, separated by a total of six games in the race for the league’s best record, could effectively distance itself from the other two and become the team to beat in the NL, because one of them could very well end up with the prized pick-up of this trade market: New York Mets outfielder Carlos Beltran.

As the swirl of rumors and speculation — a pursuit for which Twitter appears to have been invented — gains momentum in advance of the Sunday deadline, the Giants, Phillies and Braves are the apparent favorites to land Beltran, who, at age 34, is having a resurgent year for the cash-strapped Mets.

“This is a pretty stout group that is known for its pitching," Giants General Manager Brian Sabean told reporters Sunday. “Who knows? They might be . . . good enough to pull this off. [But] do I think they need help? Yes.”

Other teams are pursuing Beltran, including the New York Yankees, Boston Red Sox and Texas Rangers, but Beltran, whose full no-trade protection gives him the right to veto any deal, has made clear his preference for staying in the NL. The Mets, who have already dealt away closer Francisco Rodriguez this month, are looking for one or more top prospects in return for Beltran — although the price in talent would go down in relation to how much of the roughly $7 million still owed to Beltran the trade partner is willing to absorb.

“It’s going to be convenient for the organization, to be sure,” Beltran told, referring to the Mets getting out from under the remainder of his $18.5 million salary. “But it also has to be convenient for me. If it’s convenient for both, we move forward.”

The last two Julys have been dominated by talk of starting pitching, particularly by talk of Cliff Lee, the left-handed ace who was traded in July in both 2009 and 2010, in both cases altering the postseason landscape.

But this year, with the Colorado Rockies apparently unwilling to trade Ubaldo Jimenez and the Tampa Bay Rays sending similar signals regarding James Shields, there are no front-line starting pitchers available on the market. The best of a mediocre lot may be Hiroki Kuroda of the Los Angeles Dodgers, who is 6-12 with a 3.19 ERA and who, like Beltran, has no-trade protection.

Beyond that, the market for starting pitching is thin, filled mainly with back-of-the-rotation journeymen such as Washington Nationals right-hander Jason Marquis – one of several veterans (along with Livan Hernandez, Todd Coffey, Sean Burnett, Laynce Nix and Ivan Rodriguez) the Nationals could deal away this month.

The most ubiquitous currency in this market is relief pitching – which every contender seems to need, and every non-contender seems to have. The top reliever on the market is San Diego Padres closer Heath Bell, with the Phillies, Rangers, Los Angeles Angels, St. Louis Cardinals and Cincinnati Reds in hot pursuit.

But partly because of Beltran’s resurgence and eminent availability, and partly because so many contenders have the same need, this year’s trade market is defined by outfielders. And because there is only one Beltran, and a half-dozen or more contenders who need him, a handful of other trade-bait outfielders has emerged.

In one group is a handful of younger, more controllable (baseball-speak for “further from free agency”) semi-stars, including center fielders B.J. Upton of the Tampa Bay Rays, Colby Rasmus of the St. Louis Cardinals, Minnesota’s Denard Span and the Houston Astros’ Michael Bourn. While none would affect a pennant race as decidedly as Beltran, the Nationals, who need a long-term solution in center field and leadoff, could be among the most aggressive buyers.

In another group is a handful of veteran rent-a-bats, such as Oakland’s Josh Willingham, Kansas City's Jeff Francouer and Minnesota’s Michael Cuddyer, who could wind up in platoons for contending teams down the stretch.

But the biggest game-changer in this market remains Beltran. Seven years ago, the Astros snagged him in a trade from Kansas City and watched as he led them to the playoffs and as far as a Game 7 in the NL Championship Series. A year later, he helped the Astros to the World Series.

Beltran is no longer in his prime, and he may never repeat his 2004 postseason, when he hit eight homers in 12 games for the Astros. But he’s the biggest difference-maker out there, and he will almost certainly be making a difference somewhere other than Queens in less than a week.