Parents United, the District's influential education advocacy group, implored a sympathetic school board last night to reject Superintendent Floretta D. McKenzie's proposed austerity budget and add money for smaller classes, expanded athletics, higher teacher salaries and repairs to crumbling buildings.

At the second of three public hearings on McKenzie's proposal for a $459 million budget in 1989, the parents group urged board members to take courage from the overwhelming support voters gave to a school initiative on this month's city ballot. The initiative declared education funding to be "of the highest priority."

"The political will to do most of what we're talking about exists," said Roderic Boggs, counsel to Parents United. Boggs was one of five speakers from the group, a majority of the eight people who addressed the board's Finance Committee. The first hearing last week drew only three speakers. A third session is set for Monday.

McKenzie, who did not attend the hearing, has called her budget plan, a 6.6 percent increase over this year's budget, austere. It contains no major new programs and does not continue a policy the board set last year of reducing class size in elementary and secondary schools.

Parents United director Delabian Rice-Thurston said she was not certain how much the group's proposed additions to the budget would cost, but she said the $44 million that school administrators shaved off initial proposals by principals "would be a start."

Last night's hearing began with a videotape produced by the school system in which an announcer explained highlights of the McKenzie budget over upbeat music.

"We're a little at a loss," Parents United Cochairman Jay Silberman told the board after the showing. "We don't have any music."

Instead, the group presented results of a survey showing that 60 percent of District schools have leaking roofs, 20 percent of elementary schools have no playground equipment and 75 percent of schools report missing or broken doors.

"Our building conditions are pathetic," Rice-Thurston said. "Our counselor to student ratio of 1 to 400 is unsatisfactory."

Speakers lamented the lack of a biology lab at Banneker High School, the absence of an auditorium at Hardy Middle School, and, at Weatherless Elementary, holes in doors so large that rats and snakes have made their way into the cafeteria.

Parents United protested the lack of detail in the school system's budget books, saying that the presentation made it nearly impossible to track spending.

Board members -- six of the 11 members attended the hearing -- assured parents that they intend to beef up McKenzie's request considerably.

Nate Bush (Ward 7), chairman of the Finance Committee, said that the board will definitely add to McKenzie's budget in three major areas:Continuing its effort to reduce class size in elementary schools by trimming pupil-teacher ratios in third and fourth grades. The board began its campaign for smaller classes this year by slicing ratios in first and second grades from 25-1 to 20-1. Reducing class size in secondary schools, extending lower ratios to science and social studies classes. English and math classes were made smaller this year. Providing enough money to add several new sports, including soccer, wrestling and golf, to the intermural program. Although McKenzie included $373,000 in her proposal to reorganize the high schools athletics office, Bush said more was needed to revitalize the city's sports programs.

Board President R. David Hall said that while he agrees with the parents' goals, the school system faces a difficult political battle in a year in which Mayor Marion Barry and the D.C. Council are talking about budget cuts and tax increases.

Parents United's analysis of city budgets shows that public school financing increased by 18 percent from 1984 to 1987, a smaller proportional increase than 18 of the city's 24 largest agencies. Nonetheless, Hall predicted, the council, which must act on the school budget, "will single out the school system as the reason for raising taxes."