July 11, 1982

Hackensack, N.J., hasn't had a good time of it since the mammoth Bergen County shopping malls drained the lifeblood out of downtown starting in the 1950's. Now, in a hopeful sign of resurgence, groundbreaking should begin this month on the first phase of a major office development; the work had to await relocation of a big sewer line.

Gerard Schwarz never plays the trumpet anymore. He gave up a career as a virtuoso instrumentalist six years ago in order to conduct full time. Now he is music director of the Los Angeles Chamber Symphony and of New York's Y Chamber Symphony, which he founded in 1977, and of the Waterloo Festival Orchestra in New Jersey. He is also preparing for his opera conducting debut in Washington next season, and this summer he has taken on a new assignment - music adviser to New York's Mostly Mozart Festival, which starts tomorrow night at Avery Fisher Hall. A music adviser isn't a music director, as Mr. Schwarz and the festival's director, William C. Lockwood, are quick to assert, and Mostly Mozart's format of orchestral concerts under guest conductors alternating with chamber-music evenings will remain unchanged. Mr. Schwarz's job, a three-year appointment, will require him to take responsibility for the Festival Orchestra's personnel, morale and development, conduct about one-third of its concerts, and offer program ideas to help the festival expand. Short and energetic, Mr. Schwarz uses the word ''wonderful'' a great deal as he speaks fluently about orchestras, becoming a conductor, and the effect that he expects his appointment to have on the Mostly Mozart festival. ''I think what they're looking for in me is someone to continue to help the orchestra to grow, and to find varied and interesting repertory for the public and the critics,'' he says.

HARTFORD ALL the months of planning, speech-making and wooing of delegates will come down over the next two weekends to a few crucial roll-call votes that will shape the course of the statewide election campaigns for both parties for the rest of this year. It is state convention time again in Connecticut. Political conventions have become anachronisms in some states where the parties rely more on primary elections to choose their candidates. But here the convention system remains strong, and it is rare for a candidate for statewide office to be unseated in a primary election after winning the endorsement of a majority of the convention delegates. Amid all the hoopla of bands, banners and bunting, the two state conventions this year should offer some contrasts to each other and to the conventions of four years ago.

Negotiations for a settlement of the Lebanon crisis made little headway today, amid indications that the Palestine Liberation Organization has no intention of withdrawing from Beirut without major political concessions. Israeli armored units in the hills surrounding west Beirut traded intermittent artillery fire with the Palestinian guerrillas trapped inside, after a night of fierce Israeli shelling. Lebanon's Prime Minister, Shafik al-Wazzan, President Elias Sarkis, Foreign Minister Fuad Butros and the American special envoy, Philip C. Habib, met at the presidential palace in Baabda, overlooking Beirut, but there was no reported progress in their efforts to find a solution for the Beirut crisis and the withdrawal of the P.L.O. The negotiations have not only become bogged down, but they have become extremely difficult to follow. The present positions of the key parties, Israel and the P.L.O., seem unbridgeable, and confusion over where the negotiations stand is a result of the unusual manner in which they are carried out.

Israel has given United States intelligence officials documents and other information obtained in Lebanon indicating that mercenaries from India, Pakistan, Bangladesh and various African nations were fighting with the Palestine Liberation Organization. At the same time, the Israelis also gave American officials an account of what they considered the surprisingly large stores of weapons seized by Israeli troops in Lebanon. Among those weapons, the Israelis said, were American M-16 rifles that had been sold to Saudi Arabia. Copies of the documents, most of which were given to President Reagan late last month by Prime Minister Menachem Begin, were made available here by Israeli officials.