DALLAS -- Within a month of arriving at the Dallas FBI office in November 1988, agent Vic Houston was handed a tough assignment: Sift through a file of 3 1/2-year-old allegations and find a way to put former savings and loan executive John H. Roberts Jr. in jail.

The lines of inquiry seemed endless. Should Houston investigate the millions of dollars in loans that Roberts had made to his friends, relatives and business associates while he owned Summit Savings Association? Or should he concentrate on the millions that Roberts had borrowed from another Dallas thrift and never paid back? Then again, maybe he should go after several questionable land deals, or the unexplained transfers of Summit funds and stocks to Roberts's personal account, or Summit's hidden purchase of a company owned by Roberts.

In the end, Houston zeroed in on a scheme that seemed clear-cut and simple: Roberts's use of Summit funds to buy himself a jet airplane, which he concealed with the help of a straw borrower. It was only one piece of what appeared to be a grand puzzle of unusual transactions. But it was something Houston thought he could prove and a jury could grasp.

The Summit case, resulting in a five-year prison term for Roberts and his cooperation in investigations of other thrift owners, illustrates the prevailing theory of how to prosecute the hundreds of complicated savings and loan cases now underway: Simplify, streamline and, to some extent, deal.

Congress has stiffened bank fraud statutes and expanded the Justice Department's budget in hopes that savings and loan crooks will be investigated and prosecuted to the nth degree. But FBI agents and prosecutors have decided that when the landscape of fraud is so vast, less is often more.

"Will we ever know the totality of the criminality? Probably not," said Tony Adamski, who heads the FBI's financial crimes unit. "Could we have proceeded against people who, although not significant players, have some criminal liability? Probably yes."

As prosecutors see it, a jury can understand only so many schemes at one time. The courts can handle only so many megatrials. And some allegations are so old that agents must race to beat the legal deadlines for bringing charges.

After the first few savings and loan cases, Justice Department officials decided they had to shortcut the traditional approach to white-collar crime, where investigators start at the bottom of a pyramid and try to recreate a scheme in its entirety. Instead, their strategy is to identify those most culpable and try to tie them to discrete transactions for a "snapshot" indictment. "If you have a choice between presenting this conspiracy to defraud the institution or false entries, take the false entries," said James G. Richmond, in charge of financial crimes prosecutions for the Justice Department.

The trade-off in this approach is that it forces prosecutors to make more deals with lower-level players in order to scale the pyramid. "We need to seek the most direct route to the top," said Marvin Collins, the U.S. attorney in Dallas, home of a 125-person task force that is viewed as a model for the Justice Department's efforts. "We have to be willing to do business to a greater extent" than in other white-collar fraud cases.

A narrower indictment also may produce a shorter prison sentence if the alleged crimes occurred after the adoption of federal sentencing guidelines in November 1987. Under the guidelines, prison terms and fines increase with the dollar amount of fraud proven.

The Dallas Bank Fraud Task Force's record thus far provides an indication of the punishment being meted out. Of 45 defendants who have been convicted and sentenced, 15 received probation. Those sentenced to prison received an average term of about four years.

Nationally, 316 individuals have been convicted in major savings and loan cases that involved thrift principals, multiple borrowers or more than $100,000 in losses. About 77 percent of those convicted have received prison time. Judges have fined the defendants a total of $3.6 million and ordered $176 million in restitution.

Meanwhile, the FBI has 654 investigations underway involving losses of $100,000 or more. Attorney General Dick Thornburgh has said he expects agents and prosecutors will be working on thrift cases for five years. Plumbing 'The Black Hole'

Northern Texas has been the laboratory for S&L prosecutions. The first major case here, involving dozens of defendants, was numbingly complex. It drew a grand picture of fraud along Interstate 30 outside Dallas, involving five savings and loans and $140 million in fraudulent loans for condominium development.

More than 100 people have been convicted since a task force created specifically for this case began its investigation five years ago. But when the top seven defendants went to trial in 1989, a jury deadlocked after hearing seven months of evidence. Even before the mistrial was declared, Collins decided that he could not possibly "do another 20 cases like that."

The next indictments, handled by the Dallas Bank Fraud Task Force, centered on simpler schemes involving kickbacks from loans, false statements to regulators, tax violations and the use of thrift funds to make illegal campaign contributions, finance a private beach house or pay for prostitutes.

In a different context, at another time, Summit might have been a top priority from the moment federal regulators alerted the FBI to questionable transactions in August 1986. As it was, an agent barely had time to review the allegations and request a few subpoenas before another S&L trial demanded his attention and the prosecutor turned to a thrift with even bigger losses.

The Summit file sat for the better part of two years before Vic Houston was transferred to Dallas in November 1988. Houston was part of a wave of reinforcements ordered by Washington in response to the passionate pleas of U.S. Attorney Collins and Bobby R. Gillham, head of the Dallas FBI office.

The short, gray-haired Houston struck an unprepossessing figure at his desk in the noisiest, least desirable spot of "the bullpen" of the FBI's office. Soon, however, other agents found themselves asking him for advice. Unlike many of them, he had handled bank failures at his previous assignment in Midland, Tex. Once, he had even worked at a bank.

When Houston ordered the Roberts file from the documents room, nicknamed "the black hole," his first reaction was dismay. Although FBI officials by then had listed the case among their top five, the most promising allegation was beyond the statute of limitations. "It was very frustrating," he said. "You look at it and say, 'Why didn't we have this before?' "

The most frequent answer in Dallas those days was deregulation. In the early 1980s, 100 federal examiners had supervised 500 thrifts in five states.

But in Summit's case, regulators were unusually dogged, conducting nearly continuous examinations after Roberts, then 37, purchased Summit in November 1983 for $980,000 in cash and stock. They fell down, however, in sending criminal referrals to the FBI, waiting nearly 18 months to forward information unearthed in early 1985.

By the time Houston looked at the file, many of the allegations were nearly 4 years old. Under the statute of limitations in effect at the time, Houston had six months left to make a case.

One option was to concentrate on more recent loans that Roberts had received from two other Dallas S&Ls on the task force's list, Sunbelt Savings Association and Western Savings Association. But Roberts's dealings with them were complicated and cloudy. Robert F. Adams, the prosecutor on the case, felt the best plan was to nail Roberts on Summit transactions, then flip him to pick up new information about Sunbelt and Western.

"Our goal was to get Roberts in and pled," Adams said. "A relatively quick and simple case . . . would secure Roberts's cooperation and give us a big leg up in getting at the other owners." Running Out of Time

From 15 white referral forms sent by the regulators, Houston picked four transactions to pursue and requested 46 more subpoenas. He was so worried about running out of time that he did not read the bank examination reports, though he said "those are usually the first thing I go to."

If he had, he would have seen a rather damning portrait. "Roberts engaged in unsafe and unsound transactions resulting in personal enrichment to himself and his business associates," federal examiners said in 1987, listing 23 questionable transactions.

Initially, regulators had been relieved to see the soft-spoken, likable real estate investor from San Antonio take over Summit in late 1983 as it teetered on the brink of solvency. Roberts was handsome and energetic, always talking on his car phone, always on his way to close a real estate deal. From modest beginnings, he had amassed enough wealth to pay his wife $1 million when he divorced her the year before he bought Summit.

He also had some experience in the business; besides Summit, he owned midsized Commerce Savings & Loan in Dallas from 1982 to 1984. "We thought Roberts was someone who knew how the savings and loan industry worked and could help Summit," said Al Dermody, an assistant deputy district director for the Office of Thrift Supervision (OTS) in Dallas, the federal regulatory agency. "Live and learn."

Federal regulators watched brokered deposits flow into the institution for its high interest rates and vanish into losing real estate transactions and questionable loans. Loan files contained no applications and, often, no substantiation of what the collateral was worth, Dermody said.

At the end of a number of complex transactions, regulators uncovered signs of benefits to Roberts. One exam showed the thrift had paid $3 million for a Manhattan co-op, where Roberts lived much of the time, federal authorities said.

Another exam showed that Summit paid $581,000 for a real estate contracting firm of questionable worth owned by Roberts's brother, who had taken over Roberts's interest in the company. Examiners also reported that Summit had loaned $2.5 million to a friend of Roberts and that $117,000 of the loan went to Roberts. When regulators wrote Roberts to ask why, he did not answer.

In 1985, only two years after he bought Summit, Roberts was forced to give up his ownership. He pledged all of Summit's stock as collateral for a $10 million loan, then defaulted. Western, which held the loan, told regulators it now owned Summit. The government, already unhappy with Western, took control of the thrift, eventually merging it with seven other failed institutions in 1988. At the time, OTS estimated Summit's losses at $153 million.

Some of the criminal referrals to the FBI described what appeared to be direct transfers of more than $100,000 in Summit funds to Roberts's personal accounts, and the thrift's hidden purchase of an asphalt paving company owned by Roberts and another thrift officer. But Houston was most hopeful about a referral on a $4.5 million Summit loan to Jackie E. Hinson, who ran a private jet hanger, to purchase a Gulfstream II jet.

The whole transaction seemed fishy. Hinson's loan application was dated six months after the loan was approved. Financial records showed Hinson's salary was about $75,000 a year, seemingly not enough to pay even the interest. Other documents raised questions about the true ownership of the plane, registered in the Cayman Islands.

Houston was working on a theory of Roberts as "a plane freak," a guy who, according to friends, called for his helicopter to pick him up in the parking lot after he dined at a fancy restaurant.

Thrift officials told the regulators Summit owned a single $1.3 million jet, but Summit's insurance policy indicated that it was paying premiums for three corporate jets, plus a jet helicopter and a turboprop plane. Did Summit have a secret fleet of planes for Roberts's use?

Houston questioned Hinson, who provided some information. The agent then sought out thrift employees, asking each: "Did you do this on your own or were you instructed to do this?"

One of the more valuable witnesses came to the FBI through a fluke. A year earlier, the Dallas Times Herald had published 392 names of individuals subpoenaed by the S&L grand jury. Justice Department officials were apoplectic about the disclosure, but it brought them James Holbrook, Summit's attorney.

Holbrook, who had helped arrange the Gulfstream II loan, had not even received his subpoena when he read his name in the paper. He figured he had done nothing wrong, so he volunteered to cooperate. Simplify and Deal

The weekend before the statute of limitations ran out for some acts, the prosecutor and the agent holed up in the task force office, refining the indictment. Partly out of fear of losing the jury, Adams had decided against two of the four transactions that Houston investigated, the agent said. But the prosecutor said he liked the "sex appeal" of the airplane scheme.

The 38-count indictment charged Roberts with arranging for Hinson to buy the jet for him, then funneling Summit funds to Hinson to make payments on the Summit loan. Roberts also was charged with arranging a $95,000 loan to Hinson to refurbish the plane and with using the proceeds of other Summit loans to make payments on a Lear jet. Finally, the indictment alleged Roberts put a fictitious employee on Summit's payroll to defray his business costs.

If convicted of all charges, Roberts faced a maximum prison term of 190 years. Two weeks after the indictment, he decided to plead guilty to one count of bank fraud and one count of misapplication of funds in exchange for the prosecutor's agreement to drop the other counts. In short order, Roberts, who kept a diary of all his transactions, was testifying before the grand jury about Sunbelt and Western. Holbrook later agreed to plead guilty to one felony count.

At sentencing in January, Roberts's attorney portrayed him as a compulsive deal-maker who was undergoing counseling for low self-esteem. The judge rejected the government's request that Roberts pay $4.5 million in restitution, but gave the former thrift owner a five-year prison term.

Roberts was "floored" by the sentence and is now asking the judge to reduce it, according to his attorney, James M. Murphy. "He feels the losses attributed to him were inflated," Murphy said. At a federal penitentiary in eastern Texas, Roberts works in the prison warehouse while awaiting his first parole date in January 1992.

Arthur Leiser, former senior examiner for the Texas Savings and Loan Department, was disappointed with how the case ended. "It's a shame he was only charged with an airplane," he said.

But Adams and Houston see it differently. "It's probably not what most people think about when they think about savings and loan fraud," Adams said. "It may not be a good characterization of what Roberts did at the institution."

But, he said, "This was a case we could prove {that was} relatively simple to convey to a jury. All these guys are involved in a lot of dirty deals. At some point, you pick one and go with it."