Mayor Marion Barry, facing a weak field of challengers, kicked off his campaign for a third term at the D.C. Convention Center yesterday, warning his supporters against complacency and proclaiming that "we have learned much from our errors."

Barry, in what aides have described as a move to preempt criticism of his administration, laid claim to progress in virtually every area of city government and vowed to improve the city's troubled public housing system and expose any further corruption in the D.C. government.

"Whatever area you look at, you can see your city government works for you," Barry told a crowd of 800 to 1,000 supporters. "All of these things didn't just happen -- our nation's leading jobs program, our housing program . . . our plummeting crime rates, our balanced budgets, our downtown revitalization . . . . They only happened because I care and am committed to giving you the kind of leadership that can make it happen."

Barry, 50, who was accompanied by his wife Effi and son Christopher, delivered an hour-long speech following a color slide show and testimonials from a wide assortment of D.C. residents, including business leaders, elected representatives, labor leaders, gay activists and public housing residents.

Effi Barry, addressing her husband as "Mr. Mayor," pledged her "undying loyalty." The mayor's personal physician, Edward Mazique, pronounced that "Marion Barry is good medicine for the District of Columbia."

The long-expected kickoff event presented a scene of contrasting moods, with Barry supporters breaking repeatedly into a chant of "Four More Years!" and 5-year-old Christopher devoting most of his time to reading a book and playing with a toy GI Joe soldier.

The Rev. H. Beecher Hicks delivered a barn-burning introduction to the mayor, recounting Barry's achievements and embracing a phrase often used by Barry's critics. "He is," Hicks said to great applause, "the Teflon Mayor. You can burn it but you can't make it stick."

Barry, in several references during his speech, struck a theme that is expected to be heard often in the coming campaign, saying he wants to serve a third term because "I want one Washington for all of us."

In an interview on the eve of his announcement, the mayor suggested that the "One Washington" slogan reflects his concern that the city faces growing polarization between the races and that a principal cause is media scrutiny of his minority-run government.

"How do you bring people together in one Washington?" he asked Friday afternoon during the interview. "This town is becoming more and more polarized . . . . Part of it is black and white polarization. Part of it I attribute to the media."

The announcement speech included no references to racial polarization, concentrating primarily on the mayor's accomplishments in office and introducing what Barry said will be a campaign theme encouraging people to reduce their dependency on government.

"The dependency welfare system in this country has destroyed several generations of people, has made them too dependent on government," Barry said in the interview. "So the theme is going to be on how do you get people self-sufficient, how do you get jobs, how do you show that you care and how do you bring us all together as one Washington?"

Aides said that although the mayor has no major opponents in sight, he expects a tough campaign that will be marked by continuing media coverage of trouble spots in his administration, including government corruption and the ongoing crises in housing and the city's overcrowded prison system.

"There is going to be a serious examination of what he has done," said one aide, adding that Barry is trying to head off criticism by confronting directly the vulnerable elements of his record. "He wants to get [his message] out there."

Barry's second term has been marred by a series of corruption-related cases that have implicated several high-level Barry appointees, including his longtime aide and former deputy mayor Ivanhoe Donaldson.

Donaldson, who orchestrated Barry's come-from-behind 1978 election and directed his reelection bid four years ago, began serving a seven-year sentence in federal prison in January after pleading guilty to defrauding the District government of more than $190,000. U.S. Attorney Joseph E. diGenova said the case exposed "raw corruption" in the D.C. government.

Two months later, the Barry administration was stung by another corruption investigation when Deputy Mayor for Finance Alphonse G. Hill, the man largely credited with helping Barry straighten out the District's tangled finances, resigned following the disclosure that he accepted $3,000 in cash payments from a city contractor. A federal grand jury is continuing its investigation of the matter.

Federal prosecutors also have obtained convictions in two other major D.C. corruption cases involving a former D.C. Lottery official and developers hired for the mayor's centerpiece Bates Street housing development project. DiGenova, whom Barry has characterized as his chief nemesis, continues to focus on possible wrongdoing by Barry administration officials.

Barry, who has denied there is massive corruption in his administration and has stressed that no one has accused him of wrongdoing, repeated yesterday that the vast majority of D.C. government employes are honest.

"A government should be nothing less than 100 percent honest," he said. "I have committed our government to exposing anyone -- no matter who that person may be -- who breaks the sacred trust. A dishonest government employe has no place in the Barry administration."

Barry aides said that of all the issues facing Barry, the ethics question is the most troublesome because of its public relations impact. "The housing piece and the corrections piece are clearly problems that have to be addressed but they are tangible kinds of things you can deal with," said one aide. "The ethics thing is kind of intangible. It's much more difficult to deal with . . . .[Barry] is very concerned about it. It's a top priority."

Barry, in his speech and in the interview, stressed that he has made tangible progress in housing, asserting that "we care deeply about our public housing residents."

Federal officials have been critical of the Barry administration's efforts in housing, citing millions of federal housing dollars that have gone unspent. In addition, thousands of housing units remain unfit for habitation while about 11,000 people are on a waiting list to enter public housing.

Defending his record in housing, Barry said, "We are spending over $200 million -- with 60 percent local funds -- to renovate public housing. No other state, county or city has committed such a large share."

Barry, who in 1982 raised a record $1.3 million in campaign funds, this time appears to be in an even stronger position to win reelection. Four years ago, a host of contenders surfaced to battle Barry, including four council members and the late Patricia Roberts Harris, who had held two cabinet posts in the Carter administration.

Barry soundly defeated Harris, the leading challenger, in the decisive Democratic mayoral primary and went on to overwhelm Republican candidate E. Brooke Lee in the general election.

In 1978, then-city council member Barry himself was viewed as a long-shot candidate, taking on incumbent Mayor Walter Washington and D.C. City Council Chairman Sterling Tucker. Barry narrowly defeated them in the primary on the strength of an unlikely coalition of disenfranchised groups and white liberal supporters.

This year several well-known politicians weighed a challenge to Barry, but none has entered the race thus far. Council Chairman David A. Clarke announced last month he would not run for mayor and would seek reelection instead. Council members John A. Wilson (D-Ward 2) and Charlene Drew Jarvis (D-Ward 4) have not yet declared their intentions.

Four candidates have gotten into the contest so far: Mattie Taylor, a former school board member and D.C. employment services official; health care consultant Brian Moore; accountant Calvin Gurley and sex entrepreneur Dennis Sobin. Taylor and Sobin are Democrats; Gurley and Moore are independents.

One of Barry's opponents in 1982, Council member John Ray (D-At Large), appeared on the dais with the mayor yesterday, along with council members H.R. Crawford (D-Ward 7), Wilhelmina J. Rolark (D-Ward 8), Polly Shackleton (D-Ward 3) and William Spaulding (D-Ward 5).

The crowd was composed of city workers, department heads led by City Administrator Thomas Downs, former city officials, including former city administrator Elijah Rogers and former employment services head Matthew F. Shannon, and private business leaders such as Delano Lewis, a top executive with Chesapeake & Potomac Telephone Co., and Luther Hodges, president of the National Bank of Washington.

Following the mayor's speech, well-wishers swarmed to the dais and heroic theme music blared from the Convention Center public address system. The incumbent, pledging a vigorous campaign, told reporters he was "four years older and more pumped up" than ever.