Israel and Lebanon have agreed to open negotiations next Monday on security arrangements for the withdrawal of Israeli forces from southern Lebanon, the United Nations announced tonight.

The "conference of military representatives," convened by Secretary General Javier Perez de Cuellar, will take place at the the U.N. Interim Force in Lebanon (UNIFIL) headquarters in the border town of Naquora, the U.N. statement said.

Officials noted that the wording of the terse announcement sidestepped the procedural hurdle that had delayed the start of negotiations. It permits Israel to maintain that the talks will take place directly between Israeli and Lebanese officers, while the Beirut government can claim they are being held under the U.N. umbrella.

Jean-Claude Aime, the U.N. official who worked out the arrangements for the meeting with the Israelis and Lebanese, also held discussions with Syrian leaders in Damascus. U.N. officials here confirmed that Syria gave Beirut the green light to proceed.

The way for negotiations has been cleared for two months, ever since the new Israeli coalition government dropped its demand for a simultaneous Syrian troop withdrawal from Lebanon. Israel initially had sought U.S. mediation, but a month ago Secretary of State George P. Shultz announced that conditions did not yet exist for the United States to play a useful role.

At that time, U.S. officials indicated that Shultz remained bitter that Syria had pressured the Lebanese to abrogate the withdrawal agreement he worked out between Israel and Lebanon in May 1983. Some also conceded that an active U.S. effort during the election campaign could provide an unwelcome reminder of administration failures in Lebanon.

The Israeli Cabinet took the position this past Sunday that it still wants Washington to play some role in the withdrawal negotiations. Assistant Secretary of State Richard W. Murphy, who explored the negotiating possibilities earlier this fall, was in Israel today. But Israeli officials indicated that the extent of U.S. involvement depends largely on the Syrians.

Israeli officials confirmed that they still want informal assurances from Syria that it will not move its soldiers into the vacuum to be left by withdrawing Israeli troops and that Syria will act to prevent Palestinian guerrillas from returning to southern Lebanon. These are issues the Israeli-Lebanese negotiations are not likely to resolve, the Israelis said.

What could be determined in the talks are the timetable for Israeli withdrawal, the role UNIFIL will play in policing the area, and which other forces will participate in security arrangements to prevent attacks across Israel's northern border.

Israeli diplomats today maintained their insistence that the South Lebanon Army, a Christian-led militia armed and trained by Israel, be assigned to police the area immediately adjacent to the border, with UNIFIL troops stationed to the north and the east. Israel has suggested that by incorporating the SLA into the Lebanese Army as a complete unit, Lebanon can maintain its claim to sovereignty over the area.

The Lebanese have spoken of mustering some members of the SLA back into the Lebanese Army as individuals, but have refused to recognize it as an autonomous military unit. The Lebanese government has proposed that UNIFIL and Lebanese Army units police the border area.

U.N. officials said these positions remain unchanged as the two sides prepare for the start of talks.

"This is just a first step," said Brian Urquhart, the under secretary in charge of U.N. peace-keeping operations. "There are still lots of problems but the idea is to get them talking."

No announcement was made on the level of representation at the meeting. But one of the parties involved said the expectation was that Israel and Lebanon would be represented by their army chiefs of staff -- Gen. Moshe Levy and Gen. Michel Aoun -- and the U.N. by Gen. William Callaghan of Ireland, the UNIFIL commander.