ULSAN, South Korea, 21 June — Germany expect to be at full strength when they take on rank outsiders the United States in a World Cup quarterfinal here today which could be won in the air.

Playmaker Michael Ballack and defender Christoph Metzelder trained with the German squad here yesterday, signaling their fitness for a match the three-time winners are hot-favorites to win and reach the semifinals for the first time since 1990 when they went on to win the trophy.

Ballack’s participation had been in doubt after he strained a calf muscle in the 1-0 second-round win over Paraguay last Saturday.

The 25-year-old Bayern Munich-bound midfielder did not train on the two days afterward but resumed training on Wednesday although coach Rudi Voeller said he had been initially restricted to jogging as a precautionary measure.

But Ballack trained as normal with the squad as they tried out the pitch at the Ulsan Munsu Stadium soon after arriving from their base at Sogwipo.

“Ballack’s calf problem hasn’t returned,” Voeller said earlier on Thursday, although he admitted he was not yet 100 percent fit.

Metzelder had to be substituted after an hour of the Paraguay match with a strained left calf but he too trained here on Friday.

Germany line up with the tournament’s joint leading scorer Miroslav Klose and Voeller could opt to pair him with the towering 1.93-meter (6ft-4ins) striker Carsten Jancker to maximize the threat to an American defense susceptible to crosses. Klose has scored all five of his goals with headers.

US coach Bruce Arena said yesterday that the Germans’ size and power made them formidable opponents for the Americans, who have reached the last eight for the first time in 72 years.

“They are probably the biggest team in the tournament,” he said. “Depending on who they start they can start nine or ten players over six feet tall.

“Obviously over 90 minutes we’re going to get into a lot of battles on the field so size is a factor.”

Arena said the US team had learned their lessons from a 4-2 defeat to Germany in a friendly in March.

“We learned we’d better not be giving them a whole lot of crosses in the box where they are uncontested,” he said.

All of the US squad with the exception of defender Jeff Agoos, who is out of the tournament, trained at the stadium after the Germans.

Voeller, a World Cup winner in the 1990 team, meanwhile was in confident mood yesterday before his team flew to Ulsan.

“We are now in a position where we can get into the last four. That was our goal and it’s now a dream which we can realize. Things are looking good,” he said.

“We are really up for it — you can see that in training. We feel we have a real chance and it would be fatal to let it slide away from us.

“Against the United States we will go on the attack,” added Voeller.

“The USA have nothing to lose. That’s what makes them so dangerous.”

Karl-Heinz Rummenigge, who was a scorer in Germany’s 3-2 loss to Argentina in the 1986 World Cup final, said defeat was unimaginable. “But we must not underestimate our opponents — they are a big surprise package,” he said.

“Two years ago (after a disastrous 2000 European Championships) nobody would have thought Germany would be in the quarters with a good chance of reaching the final,” Rummenigge said.

The winner of the tie will meet either Spain or South Korea in Seoul on Tuesday in the semifinal.

If Germany reach the last four they will have done so after playing Saudi Arabia, Cameroon, Ireland, Paraguay and the unfancied Americans.