The 35-year-old, who won the last of his three international caps in June 2003, was initially seen as an emergency replacement for injured Rene Adler with Schalke 04's Manuel Neuer and Werder Bremen's Tim Wiese battling it out for the starting spot.
But Germany coach Joachim Low refused to say whether Butt, who was a replacement keeper at the 2002 World Cup and the Euro 2000, would be the third choice.
"Now is not the time for this yet," he told reporters during the squad presentation. "We will sit down calmly and discuss the situation until the end of next week and then announce our decision.
"We discussed it, but the decision (for Butt) came quickly," Loew said. "He has been part of a tournament (in 2002) and he has that World Cup experience."
Butt has been part of Bayern's successful title run and will also play in the German Cup and Champions League finals.
"He has the confidence," said Low.
EXPERIENCED BACKBONE
The Bayern keeper, who is experiencing a second wind after clinching the starting spot at his club late last season, is one of seven Bayern players to be called up, including Philipp Lahm, Holger Badstuber, Thomas Muller, Miroslav Klose, Bastian Schweinsteiger and Mario Gomez.
An experienced backbone with captain Michael Ballack, Lahm, Per Mertesacker, Arne Friedrich, Schweinsteiger and Klose is supported by a group of hugely talented younger players including Toni Kroos, Mesut Ozil, Sami Khedira and Marko Marin.
Brazil-born striker Cacau seems to have benefited from the continuing ban on striker Kevin Kuranyi, winning a spot on the preliminary squad.
His former Stuttgart team-mate Thomas Hitzlsperger though was dropped, after his switch to Lazio in the winter to recover his form failed to pay off.
Low invited a total of 27 players for the preliminary squad, which will be reduced to 23 players by June 1 for the final list.
He also called up five 'prospect' players for the May 13 friendly against Malta because of the absence of several key players from Bayern Munich, Werder Bremen and Chelsea, who still have competitive games.
Those five will not be part of the World Cup squad.
Germany have been drawn in Group D alongside Serbia, Australia and Ghana.
Goalkeepers: Hans-Jorg Butt (Bayern Munich), Manuel Neuer (Schalke 04), Tim Wiese (Werder Bremen).
Defenders: Dennis Aogo (Hamburg SV), Holger Badstuber (Bayern Munich), Andreas Beck (Hoffenheim), Jerome Boateng (Hamburg SV) Arne Friedrich (Hertha BSC), Marcell Jansen (Hamburg SV), Philipp Lahm (Bayern Munich), Per Mertesacker (Werder Bremen), Serdar Tasci (VfB Stuttgart), Heiko Westermann (Schalke 04).
Midfielders: Michael Ballack (Chelsea), Sami Khedira (VfB Stuttgart), Toni Kroos (Bayer Leverkusen), Marko Marin (Werder Bremen) Mesut Ozil (Werder Bremen), Bastian Schweinsteiger (Bayern Munich), Christian Traesch (VfB Stuttgart), Piotr Trochowski (Hamburg SV).
