The Israeli-backed South Lebanon Army released four of more than 20 soldiers from a United Nations peace-keeping force tonight amid growing pressure on Israel to force the militia to release all the U.N. troops.

An Israeli military spokesman in Tel Aviv confirmed the release of the four soldiers, which was promised earlier today by Antoine Lahad, the commander of the South Lebanon Army. But as negotiations continued throughout the day, Lahad's militia insisted that it would not release the remaining 19 Finnish U.N. soldiers until 11 of its men were freed by the rival Lebanese Shiite Moslem militia Amal.

Amal leaders refused to release the 11 militiamen, who may have defected to the Shiite organization. In Beirut, Nabih Berri, the Amal leader in Lebanon, was quoted as saying the 11 militiamen would be released if Israel freed Amal militiamen it holds prisoner or ordered the South Lebanon Army to evacuate the town of Jezzin, a Christian stronghold in southern Lebanon that is being defended by the Israeli-backed militia.

In Washington, U.S. officials said they were in touch with Israel but generally were relying on Israel to work out the problem, since it has direct influence over the South Lebanon Army, staff writer Don Oberdorfer reported Saturday.

State Department spokesman Ed Djerejian said Friday that in general "there is no justification for kidnapings" in the area. He said that "UNIFIL has contributed significantly to the security of southern Lebanon" and that the United States "deplore(s) any acts of violence against UNIFIL troops who are engaged in continuing efforts to help the Lebanese people."

Meanwhile, Israeli Prime Minister Shimon Peres and Foreign Minister Yitzhak Shamir telephoned their counterparts in the Finnish government to pledge that Israel would do everything possible to gain the release of the Finnish soldiers, according to an Israeli Foreign Ministry spokesman.

The spokesman, Ehud Gol, also said that Israel had received assurances from the South Lebanon Army that the U.N. soldiers would not be harmed. Yesterday, the Israeli-backed militia threatened to kill some of the captives if its demands were not met.

In Helsinki, the Finnish Defense Ministry announced that Peres and Shamir also had pledged that Israel will look after the "lives, health and safety" of the Finns, The Associated Press reported.

Timur Goksel, the spokesman of the United Nations Interim Force in Lebanon (UNIFIL), said four of the soldiers were being held in the village of Qantara by about 70 South Lebanon Army militiamen who were accompanied by four Israeli Army advisers. These captives included a Finnish officer who was released yesterday to convey the South Lebanon Army's demands and then rejoined the other Finnish soldiers, Goksel said.

UNIFIL sources in Lebanon said the freed Finn, Col. Venni Hakala, was commander of the 490-man battalion, special correspondent Nora Boustany reported from Beirut. A source said he had "been physically assaulted all over his body" by several of the militiamen.

Another 19 Finnish soldiers were being held in Aadaisse, less than a mile from the Israeli border, and Goksel said several Israeli Army officers were present in the village.

Israeli radio had reported earlier tonight that Lahad said he would free the four soldiers being held at Qantara as a good-will gesture but would continue to hold the other 19 until his demands were met. One of the four released soldiers reportedly was Irish, and it is unclear whether he had been counted among the 24 Finns originally reported seized.

Goksel said the United Nations established radio contact during the day between the South Lebanon Army and the leader of the 11 militiamen, who reportedly were in the port city of Tyre. He said South Lebanon Army commanders demanded a face-to-face meeting with the militiamen, but there were "no takers for that idea."

Throughout the day, Israeli military officials insisted that they were "under restrictions" preventing them from intervening directly in what one military spokesman said was "obviously an internal Lebanese" matter.

The Israelis also appeared tacitly to support the South Lebanon Army's demands and its charge that the U.N. soldiers assisted Amal in capturing the 11 militiamen.

A military spokesman in Tel Aviv said that an Israeli commander told the UNIFIL commander, that if U.N. forces helped gain the release of the 11 men, Israel would be willing to exert pressure on the South Lebanon Army to free the Finns.

The origins of the incident, which began at about noon yesterday, remained murky today. The South Lebanon Army charged that Finnish soldiers attacked and disarmed the 11 militiamen before turning them over to Amal.

The South Lebanon Army retaliated by taking over a Finnish U.N. checkpoint at Qantara and later capturing 19 Finnish soldiers who were on a bus returning them from a visit to Israel.

However, there were other reports that the 11 militiamen surrendered to the U.N. troops and asked their assistance in reaching Tyre, which is under the control of Amal.

Special correspondent Boustany added from Beirut:

A seven-truck supply convoy was able to enter the besieged Burj al Barajinah refugee camp despite serious cease-fire violations.

Five trucks carrying food and two water tank trucks made their way into the settlement, which has about 20,000 residents, after three mortars crashed in. One exploded, killing five children instantly and seriously wounding eight others.

Meanwhile, according to reports from the northern port city of Tripoli, rival pro-Syrian and pro-Palestinian militias exchanged machine-gun and rocket fire today, killing at least 10 persons.