By Andrew Stern

CHICAGO (Reuters) - Much-anticipated testimony this week by David Radler, the ex-partner of former media baron Conrad Black, will likely make or break the criminal case against Black and three fellow executives, lawyers said.

The trial, which is entering its eighth week, will reach a crescendo when Radler, who was once operations chief at Hollinger International Inc., takes the witness stand some time on Monday and then faces what is sure to be withering cross-examination from each of the four defendants' lawyers.

Federal prosecutors get first crack and will try to paint Radler, 64, as Black's co-conspirator in skimming $60 million (30 million pounds) from Hollinger as the two dismantled the Chicago-based company they had built into one of the world's largest newspaper publishers.

Radler, a Canadian living in Vancouver, pleaded guilty nearly two years ago in exchange for a 29-month sentence and a promise to testify for prosecutors.

Just before the trial began in March, Radler also agreed to pay $29 million to settle with the U.S. Securities and Exchange Commission and paid millions more to settle with Hollinger's successor company, the Sun-Times Media Group.

The Canadian-born Black, 62, is charged with fraud, racketeering, money laundering and obstruction of justice. He faces up to 101 years in prison, millions in fines and $92 million in forfeitures if convicted.

"Without Radler, they can't prove intent," said a lawyer involved in the case who requested anonymity.

"Radler is going to have to be extremely specific about the conversations he had with the defendants and how they planned to get away with this," said Chicago attorney Hugh Totten, who has defended executives and is observing some of the trial in U.S. District Court.