Under grey skies and with fall's academic feeling in the air, thousands of alumni went back to class yesterday.

Scurrying to symposia, precious tickets carefully clutched, the alumni and visitors got their chance t sample Harvard's current academic flavor. The first of 106 academic symposia got underway yesterday.

With topics as dissimilar as the future of they city and the future of particle physics on the agendas, Harvard is billing the symposia as the meat of the celebration.

Most symposia tickets were sold out by mid-July, and the seminars were usually full.

With two more days of lessons to go, those gathered in Cambridge have a few more chances to learn what they've forgotten since they left.

Saudi Oil Minister Sheik Ahmed Z. Yamani refused to call the steep plunge in oil prices this year a total "oil price collapse," but said that "what the oil industry badly needs is price stability in the long term," during a speech yesterday at the Kennedy School of Government.

Yamani urged all oil-producing nations to prevent constant fluctuations in world oil prices by collectively establishing a price structure based on the long-term equilibrium between supply and demand.

Yamani, a 1960 graduate of Harvard Law School, made his comments before more than 650 spectators at a symposium entitled "Oil Markets: Past, Present and Future--Personal Reflections of His Excellency Ahmed Zaki Yamani."

The oil minister said oil-pricing by OPEC and non-OPEC nations based only on short term supply and demand trends led to the dramatic fall in petroleum prices from more than $30 per barrel in 1980 to a low of $9 in July 1986.

In response to an audience question, Yamani said his comments would anger some of his peers, but that a majority of OPEC members were coming around to support his thinking.

Yamani criticized calls for import restrictions on oil saying they "can lead to trade wars and spell the end of free trade practices."

"Producers as well as consumers should adopt policies that shun drastic inteference in the market forces which may disturb the much sought for long-term stability," he said. "It is only through the achievement of long-term free market equilibrium that stability can be [attained]."