With the All-Star break now receding in the rearview mirror, young men’s fancies – and old GMs’ lustful desires – will now turn to the Holy Grail of the baseball’s midseason, the decisive deadline-day trade. Unlike most quest-objects, this one isn’t wholly mythological, for the DDT does sometimes grant a contender the chance to acquire a star at small cost or to reinvigorate its quest for the pennant.

But with most deadline trades, neither benefit is automatic; most often very little changes, as in the case of the Yankees’ July 31, 2003, trade for Aaron Boone. One postseason at-bat aside, Boone was a bust; the Yankees rolled on in spite of him, as if the trade hadn’t happened. It takes a killer DDDT, such as Houston’s July 31, 1998 acquisition of Randy Johnson (in exchange for Freddy Garcia, Carlos Guillen, and John Halama), to produce a really big change. In Houston’s case, they played .596 baseball before Randy, .860 baseball with Randy.

In fact, very few deadline deals in recent years have produced a dramatic change in the pennant race, with the exception of last year’s flurry of moves by Red Sox GM Theo Epstein. In 2004, only one division lead changed hands after the deadline, with the A’s yielding to the Angels. The A’s made their only major deal, for Octavio Dotel, five weeks before the deadline. The Angels did not make a trade during the 2004 season.

The Dodgers made the biggest splash at the deadline last year, dealing Paul Lo Duca, Guillermo Mota, and Juan Encarnacion to the Marlins in exchange for Hee Seop Choi, Brad Penny, and Bill Murphy; they were four games worse after the deal than they were before. The team that made the best pennant run, the Astros, surged from 51-52 to 92-70 to take the wild card. They had made their big trade in late June, acquiring Carlos Beltran.

In this light, teams must be wary of overreaching. Except in the rarest of cases, the addition of just one player over the last eight weeks of the season will not change the outcome of a race. But in trying to load up for the stretch run, teams risk burning the franchise for years by depleting it of prospects.

While Mets fans are still smarting from the infamous Scott Kazmir-for-Victor Zambrano deal last summer, Yankee fans might recall the notorious deal struck with the Orioles on June 15, 1976. The Yankees were in first place, leading the American League by 5 1/2 games, but management felt insecure. In a true blockbuster, Yankees Rudy May, Tippy Martinez, Dave Pagan, Scott McGregor, and Rick Dempsey were sent to Baltimore in exchange for Ken Holtzman, Doyle Alexander, Grant Jackson, Elrod Hendricks, and Jimmy Freeman. Although Alexander and Jackson pitched very well in New York, the team improved by just one game over the rest of the season. By that winter, both pitchers had departed as free agents; meanwhile, McGregor, Martinez, and Dempsey would be of use to the Orioles for years to come.

The watchword for the 2005 Yankees and Mets, then, is caution. The Yankees, though much-improved of late due to the weird renaissance of Jason Giambi, still need help in center field, where their players are either too young or too old, and on the injury-depleted pitching staff. This is a weak year in the American League East, and a division title certainly seems attainable, but what then? At year’s end, ring or no ring, the Yankees will be an old team in need of rebuilding. If the team’s creditable young players have been dispersed on July 31, next year’s outlook will be that much shakier.

At this stage, it seems clear that most members of the Yankees’ operating politburo are firmly opposed to trading prospects for vets. What is unknown is what George Steinbrenner will do; in the past, the Tampa wild card has not hesitated to mortgage the future. It remains doubtful that the Yankees can acquire a strong starting pitcher, without dealing at least one of the two young players – Chien-Ming Wang and Robinson Cano – who have made such a strong impression this year.

The Mets are a .500 team in a weak division. Unlike the Yankees, who remain close to the leaders, the Mets have four teams in front of them and an eight-game deficit to make up. The four-game set with the Braves that began last night will say more about their chances, but for now the Mets need to be sellers, not buyers, in hopes of healing the damage done to the farm system at last year’s deadline.

Mike Piazza, in the last year of his contract and probably ticketed for the American League next year, could add some stretch-run pop to a team like the Texas Rangers, acting as both a backstop and designated hitter. The Rangers also have some prospects who could be attractive to the Mets: righthander Thomas Diamond, first baseman Adrian Gonzalez, catcher Gerald Laird, and infielder Ian Kinsler.

The Mets know that the trading deadline promotes delusions of grandeur. No one or two players could save last year’s team. The same is true now. They need to hold fast to that notion or risk taking another giant step backward while pretending to be going forward.