The federal trial of Catherine Duffy Petit and four co-defendants opened today at U.S. District Court in Portland, with the prosecution painting Petit as the ringmaster of an alleged $7 million fraud, while the defense pointed the finger at a Lewiston lawyer who has pleaded guilty to criminal charges and is testifying for the government.

Petit's attorney, David Beneman of Portland, wasted no time in telling jurors who the defense would implicate as the organizer of a fraud which left a wake of victims across the state.

''Thomas Blackburn is the criminal in this case. Catherine Petit is a victim of Thomas Blackburn,'' he said in his opening remarks.

Blackburn is one of six men who have pleaded guilty to a variety of charges and are scheduled to testify as part of their plea agreement for a reduced sentence. He was Petit's former attorney.

In his opening statement, Assistant U.S. Attorney Donald Clark, one of two prosecutors in the highly-anticipated case, told jurors that ''this case is about a scheme to raise money for Catherine Duffy Petit,'' as he outlined the government's 87-count conspiracy, mail fraud, money laundering, bankruptcy fraud and securities fraud case.

Petit, 52, the former owner of the Old Orchard Beach Pier, sat at the front of the courtroom flanked by attornies Beneman and Jim Lawson of Boston.

Behind them, co-defendants Paul Richard of Lewiston, Roland Morin of Lewiston, Steven Hall of Standish and his brother David all sat with their attornies. With the exception of Bruce Hochman, David Hall's attorney, they all told the jury that the evidence would fail to implicate their clients.

Clark told jurors and a courtroom packed with represenatives of Maine's media and supporters of the defendants that Petit was an active participant in spearheading a fundraising effort to support her 14-year long effort to win her civil suit against Key Bank.

Petit brought suit against the bank and co-defendants Bernstein, Shur, Sawyer & Nelson, a Portland law firm, for their alleged coercision which led to her losing ownership of the venerable Old Orchard Beach Pier.

The law firm settled with Petit in 1990 for $3.9 million. The suit against Key Bank was dismissed by summary judgement in 1995, but the Maine Supreme Judicial Court overturned that decision in December, 1996.

Clark and co-prosecutor Paula Silsby then called Frank Corrao and Joan Roberts as their first two witnesses. Corrao, a schoolhood friend of Paul Richard and the former owner of a Lewiston concrete and construction company, told the court that he agreed in 1989 to lend Petit $120,000 at the behest of Blackburn.

He was repaid most of that money after the settlement with the Portland law firm in 1990, he told the court. He also added that he was not aware that a Boston law firm handling settlement claims had authorized a payment of $127,000 to him, saying that Blackburn wrote him a check for far less.

''I can only say that I didn't get all that money,'' Corrao said. '' He's a lawyer,'' he said of Blackburn. ''He's supposed to be honest.''

Roberts, a Sabbatus resident, testified that she and her husband Charles initially invested $150,000 in 1990 after hearing of the investment from Corrao. From 1990 to 1994, she arranged for a number of friends and family members to invest, she said, to support Petit's lawsuit.

''She didn't want anymore than she needed,'' Roberts said of Petit. ''She wanted it all to end, to get it into court.''

Roberts told the court that she developed a friendship with Petit over the years and when she called her in August, 1997 to say that the FBI had scheduled to interview her the next day, Petit told her not to lie.

After hearing a number of objections from Richard's attorney, Evan Slavitt, regarding government exhibits, U.S Chief District Court Judge D. Brock Hornby asked Roberts to step down to resume testimony on Tuesday.

In his opening statement, Slavitt told the jury that Richard, 57, had heard about Petit's effort to fight against Key Bank and was drawn to help her.

''He got to know a woman wronged and it touched him,'' Slavitt said.

Slavitt said Richard started a company called H.E.R. Inc. with James Erskine, a government witness who has pleaded guilty to charges and is expected to testify, and Steven Hall in order to sell distressed real estate and raise funds for Petit.

The prosecutors allege that H.E.R. Inc. was a conduit that raked in $700,000 in illegally obtained funds. It was issued a cease and desist order by the state Attorney General's office in 1995 in their civil suit against the defendants.

That suit is pending the outcome of the federal trial. The state did reach an agreement with Sun Life of Canada to pay $2.3 million to cover losses incurred by their clients. Both Steven and David Hall were Sun Life insurance agents.

At the beginning of the proceedings, which culminate from an original 344-count indictment issued by a federal grand jury in August, 1997, Hornby told the 12 jurors and four alternates that they would be deciding a case which also involved the complex matter of bankruptcy.

Petit was placed into involuntary bankruptcy in 1994 and her estate, which lists the Key Bank suit as its only real asset, was placed in the hands of a trustee.

However, Beneman reminded jurors that her corporations, the Old Orchard Ocean Pier Co. and Whiteway Amusements, were not enjoined by bankruptcy and were litigants in a separate civil suit against the bank.

In his opening statements, Clark told the jury that Petit had committed perjury on three separate occasions in statements in U.S. Bankruptcy Court where she denied that she was raising funds to support her civil lawsuit.

After the trial, Petit's daughter, Loren Petit Cimenian of Belmont, Ma., told the assembled media that the family is relieved to see their day in court.

'' My mother has spent 14 years fighting all this,'' she said. ''Finally, we get a chance to tell our side and a chance to let people see the evidence which will prove her innocent of all these charges.''

January 25, 1999, 5:35 p.m.