All Gale Conard and his fellow blind vendors want is what a judge says the District owes them -- $620,526, to be exact. Today they are descending on Mayor Sharon Pratt Dixon's doorstep in hopes of getting it.

In what their attorney, Robert Humphreys, says is a last-ditch attempt to get the District to pay its debt, dozens of the city's blind vendors will gather at 9:30 this morning outside the District Building, then trek up to the fifth floor to meet Dixon. They have a message.

"We are asking for your assistance in righting one small but important wrong visited upon the city's blind vendors by the previous administration," says a letter they plan to present to her. "That administration quite literally robbed the blind."

Dixon spokesman Vada Manager said yesterday that Dixon won't be there, but that a representative would accept the letter.

Today's confrontation is the latest chapter in a story that began seven years ago and ended -- or so the vendors thought -- with a ruling last April by U.S. District Judge Oliver Gasch. The judge found that the District had mismanaged the program for the roughly 80 blind vendors operating in city and federal buildings in 1985, and that the vendors paid hundreds of thousands of dollars for services they never got. He told the city to repay them.

The city hasn't; in fact, it has appealed the ruling. Claude Bailey, a spokesman for the D.C. Corporation Counsel's Office, said yesterday that his office believes the vendors were wrong in taking the case to court, and that their claims could have been resolved administratively.

At issue in the lawsuit is the Randolph-Sheppard Act, a 1936 law that gives blind vendors preference in running snack bars and vending machines in federally owned or leased buildings. The law authorizes states and the District of Columbia to appoint nonprofit agencies to oversee programs.

The job of those agencies is to make sure the vendors are trained to run a small business. They also collect money from vending machines in buildings subject to the law, line up cashiers and other workers to help vendors run their shops, and provide accounting services.

The District program is supported by a percentage of the net profits paid by the vendors to the city, an amount Humphreys says averages $500,000 a year. Out of that, the city pays the management agency.

Until 1984, the local program was run by a nonprofit group, District Enterprises for the Blind. But in September 1984, the District abruptly canceled the group's contract. Three months later, it awarded a contract to DAC Corp. -- a for-profit food services firm run by Carthur Drake, a longtime supporter and close friend of then-Mayor Marion Barry.

The news shocked vendors, including Conard, who has run a snack shop in the U.S. Information Agency building for nine years. At 54, Conard has been blind since he was 5, the result of a bout of mastoiditis.

"We knew Drake was a friend of {Vernon} Hawkins," then acting head of the D.C. Commission on Social Services, Conard said. "It was quite a while later that we learned he was a friend of the mayor's."

Drake denied yesterday that the contract was an act of political favoritism. He said his firm was unpopular with the vendors because it insisted on businesslike practices, and that many vendors were not reporting all of their income.

Humphreys argued that DAC should have been prohibited from managing the vendor program because federal law requires that the managing agency be a nonprofit organization. He says today that District officials ignored him. Drake says that the deal was legal, because the city could be seen as a nonprofit group that subcontracted DAC.

Many vendors said DAC did nothing. DAC "did not do an adequate . . . job of accounting," Conard said. "They lost track of some of the insurance. They didn't do a good job of collecting and maintaining the accounts."

In September 1985, as a result of the complaints, DAC's contract was canceled. In 1988, the vendors filed suit in federal court. After a trial in December 1989, Gasch concluded that "DAC {had} spent money for consultants, additional staff and increased management service expenses," and delivered "no appreciable services."

Humphreys said he doesn't know if today's demonstration will yield any results, but that he hopes the group can appeal to Dixon's reformist image.

"We urge you to be our champion," the vendors' letter says. "Restore that which belongs to us."