By Braden Phillips

BARCELONA, Sept 17 (Reuters) - Barcelona embark on a new Champions League campaign on Wednesday against Ajax Amsterdam determined to vary their style of play amid suggestions they have become too predictable in attack.

"We've been playing the same way and Tata (coach Gerardo Martino) wants us to make some changes," Spain defender Gerard Pique told reporters on Tuesday.

"We need more time. We're trying to find the balance between playing more directly and playing as always. But things are going well," he added on the eve of the Group H tie against Ajax, the first meeting of the two former European champions.

Barcelona's signature style of quick, short passes - dubbed 'tiki-taka' - and dominant ball possession proved a successful formula under coach Pep Guardiola from the 2008-09 season.

Since then the Catalan club have won two Champions League crowns and four La Liga titles. But critics declared Barcelona's eminence over when they were humbled 7-0 on aggregate by Bayern Munich in the semi-finals of last season's competition.

Pique said Barca's rivals now "know what we are going to do", which is making victories harder to come by. "We need to find new ways to attack," he explained.

The Catalans have begun their La Liga title defence with four wins in four matches but defensive lapses in the second half, especially in Saturday's 3-2 victory over Sevilla, have made them vulnerable.

"On dead balls we have problems covering in zone (marking) or man-to-man," said Martino.

But the Argentine, who took over from Tito Vilanova before the start of the season, added: "It's not a problem of defence but of physical strength.

"Given that we cannot change that, we have to defend as best we can."

Martino wants Barca to show they can use a more direct attacking style with longer passes. But this major adjustment carries the risk of losing possession more often and leaving his players having to make more covering, defensive runs.

"They (have) had to run backwards a lot," Martino said. "We need to be more solid for everyone to run a little less."

The club announced after the news conference that Martino's father had passed away in Argentina but the club said he would stay in Barcelona for the Ajax match.

He plans to leave the following day to attend the funeral. (Editing by Stephen Wood)