It was, in many ways, a classic case of caveat emptor - let the buyer beware - said D.C. Superior Court Judge Alfred Burka after he had acquitted a Fairfax County couple of conspiracy to defraud and other charges in connection with their roof repair business.

After three days of trial and testimony by 25 government witnesses - all of which followed a two-year investigation by the D.C. police Consumer Fraud Unit - Burka said all the government had proved was that the roofers had done shoddy work - not that they had committed any crime.

"The criminal courts cannot be used as revenge for persons making a bad deal," Burka said during a hearing yesterday.

"This is a depressing situation, but . . . I, as a judge, am obliged to do my duty," he said. With that, he granted a defense motion for a judgement of acquittal in the case of the United States versus Cecil C. and Ann M. Nichols, and dismissed the 12-member jury.

The case turned on the finer points of the law of false pretense - generally whether the Nicholses had done the repairs, as government witnesses testified that they said and whether they intended to live up to lengthy warranties that went along with the deals.

Under current law here, however, Burka told the lawyers, false pretenses does not include promises - like warranties - even if there never is an intent to live up to the promise.

"I only hope the law is changed quickly to cover this situation," said Burka. Later, a spokesman for the D.C. Law Revision Commission, which is readying recommendations for a major overhaul of the city's criminal code, said proposed new laws would include a broad provision that would involve promises - such as warranties - in fraud laws.

Furthermore, Burka said, in explaining why he took the case away from the jury, there was "little more than a scintilla of evidence" of false pretenses in the government's case.

Government witnesses said they paid the defendants for leaks they said they fixed, only to discover during the next rainstorm that the repairs were made properly. Other witnesses said they discovered what they described as the poor quality of the work upon their own examination of the job or when other repairmen were called into survey the work. In another case, a new roof was improperly installed, the government contended.

Burka acquitted the defendants before any evidence was presented in their behalf.

"There would have been false pretenses if they (the defendants) collected money and no work was done," Burka explained in an interview after the hearing. But the testimony, Burka contended, showed only that some work had been done - albeit poorly.

"The government presented no evidence" about standards of work in the roofing trade, Burka said, and thus the jury, in the judge's opinion, had no way to determine whether the defendants knew, or should have known, that their work was poor.

In all 11-count indictment handled down last August, the government charged that the Nicholeses and their son, Michael P. Nichols, told customers the work on their homes and buildings had been completed when they allegedly knew the work was superficial, incomplete, or done at all.

The indictment said the family conducted the business under various names between January 1975 and last April. The individual defendants used various aliases in the course of the business, the indictment said.

Michael Nichols, 20, who was to stand trial with his parents, failed to appear in court. A bench warrant was issued for his arrest, the U.S. attorney's office said.

The government still has the option of prosecuting the younger Nichols.

The defendants were charged with conspiracy to defraud - through false pretenses and other actions - as well as on individual counts of false pretenses, grand larcency and larcency after trust.

Assistant U.S. Attorney Steven Gordon argued that the government - through a series of complaints - had shown a pattern of conduct that constituted a scheme to defraud on the part of the defendants. From the use of aliases and various company names by the defendants, the jury could infer criminal intent to defraud, Gordon argued.

The couple's overall conduct, the couple's overall conduct, the government argued, went beyond the case of a repairman who simply does a poor job.

The heart of the government's case, Gordon told Burka, was the representations made by the roofers that the repairs had been done when they "knew they had done no work or only superficial work."

"People in the District of Columbia have a right to rely on representations made to them by other people . . that those representations are not knowingly false," Gordon told the judge.

Burka was not convinced. There was proof, he said, that the mother, father and son had worked together, and that their work was not entirely satisfactory, but that does not constitute a crime.

"I'll tell you, I don't feel like I committed any crime," said Cecil Nichols as he left the courthouse.

With the "thousands of jobs a roofer does, you can't satisfy everyone," he said.