For U.S. Attorney Joseph diGenova, 1985 will probably go down as the year he finally made some headway in making District Mayor Marion Barry and his government look bad. For Barry, the early days of 1986 may be recalled as the time his psychological advantage in the city began to slip a bit.

Several major scandals have touched Barry and his administration in the last few years.

The first was the lengthy trial and later conviction of Barry's former wife Mary Treadwell, former head of the Youth Pride job training program.

Treadwell was found guilty of conspiring to defraud the federal government and the tenants at the Clifton Terrace apartments of thousands of dollars. Although Barry and Treadwell were married during part of the time when, according to the jury, Treadwell engaged in the conspiracy and made the false statements to the U.S. Department of Housing and Urban Development, Barry was not implicated in the investigation.

When Treadwell was sentenced to a three-year prison term in June 1984, diGenova said it was a message that people in high political places who commit crimes are going to be dealt with. "Treadwell demonstrates that people who are not lowly can also meet at the bar of justice," he said. But to many observers, the words of the city's chief prosecutor seemed to contain a special venom for Barry.

The second scandal involved Karen K. Johnson. A D.C. government employe, she was charged with selling and possessing cocaine.

During the investigation by diGenova's office, federal prosecutors presented evidence to a grand jury from a secretly taped conversation between Johnson and a government informant in which Johnson claimed that she had sold cocaine to Barry.

Confronted with the accusation, initially Barry said he barely knew Johnson, but later Barry's attorney acknowledged that the mayor had a "personal relationship" with her. In the cat-and-mouse game between diGenova and Barry, diGenova repeatedly stated that Barry was not the target of a grand jury investigation. At the same time, information was leaked from diGenova's office contradicting that.

Angrily comparing diGenova's investigation to bygone efforts by whites to destroy black leadership, Barry said at the time, "They used to just lynch people by rope a long time ago. After that, they're trying to lynch black people another way, and I'm not going to be lynched."

At that time, a lot of Washingtonians sympathized with Barry, and he received a great deal of support from around the city. For while Johnson received a four-month prison term, Barry was not further implicated.

But in the waning days of 1985, the Barry administration's biggest scandal came when Ivanhoe Donaldson, former D.C. deputy mayor for economic development and a longtime Barry friend and political confidant, pleaded guilty to stealing approximately $190,000 systematically from the city government in 1981 to 1983. At the time, diGenova said the case represented "the tip of the iceberg."

DiGenova expanded on that charge when Donaldson was sentenced on Jan. 27. He said the ex-deputy mayor's case exposed "raw corruption" in the District government.

Barry angrily denied that charge, saying that there "is no massive corruption . . . in this government." The mayor charged that diGenova "talks more than he produces" and had prolonged the investigations of corruption in the D.C. government in an attempt to discredit him.

But when Barry put four employes implicated in the Donaldson case on administrative leave -- with pay -- it struck many residents as doing too little, too late. One of the officials placed on leave was Matthew Shannon, director of the city's Department of Employment Services.

Meanwhile, late last week, diGenova's office struck again. It was disclosed that a federal grand jury here is investigating whether the head of a Chicago-based accounting firm gave kickbacks or other financial incentives to D.C. Deputy Mayor Alphonse G. Hill in return for receiving work on city contracts. Hill has vehemently denied the charges. But many skeptics are taking a wait-and-see attitude.

After three years of almost a scandal a year swirling around the District Building, many city residents have been changing their attitude toward the Barry administration in the last few weeks. Donaldson's crimes -- orchestrating a cover-up and using innocent subordinates, relatives and friends in his schemes and stealing from the employment services administrative fund -- hit people where they live.

Some District residents aren't as willing as they once were to blame diGenova, who is white, with pursuing a vendetta against a black administration. Now some are asking who will be the next Barry administration official accused of corruption.

In putting Donaldson, one of Barry's most trusted confidants, behind bars, diGenova won a psychological advantage that Barry had always had in the past.

The danger for Barry, which is now emerging, is that District residents are starting to lose faith. A serious erosion of confidence could be translated into votes at the polls, and many candidates are said to be waiting to take advantage of any Barry political vulnerability.

"As long as there are suspicions about massive corruption," Barry said the other day, "it masks all the positive things we have done." Despite the accuracy of that statement, the faith that many D.C. residents had built up from the impressive gains Barry made in so many other areas is waning. And the question they are asking is: "What are you going to do, Mr. Mayor?"