In case anyone forgot that today was the first day of classes, music started blaring from the schools' loudspeakers at 7:30 a.m, a slightly tinny recording of a children's choir.

By 7:45, the streets in one Moscow neighborhood were filled with scurrying parents shepherding anxious children to one of three schools within six blocks. Most of the parents brought along their cameras. All the children -- the boys and older girls in blue suits, the young girls in brown dresses with white aprons -- brought flowers for their teachers.

A grandfather, decked with medals, apparently got the wrong school. As the clock approached 8, his charge -- her face pinched with worry under hair tied tight in big white bows -- set him straight and they got to the courtyard on time. When the music stopped, the ceremony began, a full-fledged ritual complete with national anthem, a friendly lecture from the school principal, a procession of flags and presentations until at last, the 10th graders escorted the first graders up the stairs and into the school for opening day's first class -- a "lesson in peace."

Sept. 1 is the beginning of school in the Soviet Union. Today (Saturday is a school day), as 58 million students took their places in institutions ranging from kindergartens to universities, the tradition varied in only two respects.

This year for the first time, Sept. 1 was declared an "all peoples' holiday" -- officially "the day of learning" -- which meant the city was decked with Soviet flags and banners.

It also marks the launching of the Soviet Union's latest and perhaps most ambitious school reform. Destined to take 12 years to accomplish, it does not begin in earnest until 1986, when the age of enrollment drops from 7 to 6 nationwide, adding an extra year to the 10-grade elementary and secondary school system.

The main goal of the reform, openly debated in the press earlier this year, is to prepare students for work at an earlier age and to direct their training toward practical goals. It will be accompanied by additional emphasis on ideology.

"The young people, who have finished their secondary education, must be well aware of the specifics of the present stage of social development, possess class self-consciousness and be able to uphold our ideal and give a firm rebuff to hostile ideology," said Politburo member Gaidar Aliyev in a speech on school reforms to the Supreme Soviet last April.

The reform begins this year with small steps, so small that parents and students interviewed recently were not sure what to expect. According to published reports, teachers this year are expected to omit "secondary" or "complex" materials from certain textbooks which are "now written in so involved and oversophisticated a manner as to puzzle a professor sometimes," said Aliyev. It is also to add a new course on "the ethics and psychology of family life."

A push for more vocational training also begins in the higher grades this year, anticipating a decision next January on lowering the minimum working age, to allow people under 16 to operate certain farm machinery.

"The proposed reform will help gear education and character development at school to the economic activity of the nation and to make vocation-related studies a major component of school life," said Aliyev.

Western analysts have attributed the push for reforms, begun under former president Yuri Andropov, in part to the Soviet Union's labor shortage and to its need for skilled workers.

Other long-term changes envision consolidation of general history courses with courses on Soviet history, the introduction of computer science in the higher grades and a requirement that each secondary school graduate be taught to speak Russian fluently, without "impinging" on other languages native to the Soviet Union.

It also anticipates a change away from a system that graded schools according to pupil performance, known as "the percentage mania," that encouraged teachers to raise grades.

Six million teachers this year will feel the most immediate impact of the reforms with salary raises of between 30 and 35 percent, the Soviet news agency Tass reported this week.

A salary raise for teachers, some of whom were critical of the early reform proposals, is one way of making the program more popular. Other measures, apparently designed to answer concerns about the new entry age of 6, will upgrade teaching standards and ensure a regular supply of "high-quality food products" in kindergartens.

One million 6-year-olds are already enrolled in Soviet schools and this week more joined the ranks as the lower enrollment age took effect in the republic of Georgia.

Reforms were far from the minds of parents and children this week as they threw themselves into the mad rush of getting ready for school.

At Detsky Mir, a children's department store, lines formed for boys' uniforms and crowds hounded salesclerks for 4-cent pencils, $17 satchels, 20-cent notebooks and other items.

From interviews with a half dozen parents, the cost of getting a child ready for school ranged from 40 to 50 rubles, or between $50 and $61 at the current rate of ex- change, from uniforms to a year's supply of notebooks to the broad nylon white, black and brown ribbons to make the traditional bows.

On the last day before school, shortages -- and lines -- were common. A woman who had to come back into the city for a last-minute purchase had another problem. She had bought her son's uniform earlier in the summer, only to discover, when he came back from summer camp, that he had outgrown it.