Beirut — Lebanon's fragile peace is gradually unraveling, creating fears of a breakdown if there are no moves soon to consolidate the country's 179th cease-fire in the last decade.
Several developments do not bode well for the 10-day-old truce:
* The newly formed military committee has not yet agreed on means of monitoring the truce.
* Renewed fighting flared in Beirut's southern suburbs between the Lebanese Army and Muslim militiamen, reflecting the high state of tension.
* The government has not yet won agreement on a venue or agenda for the proposed ''national reconciliation conference,'' which Western and Arab mediators had hoped would commence no later than this week.
* Druze leader Walid Jumblatt has announced his Progressive Socialist Party will set up a local administration in the Druze-dominated Shouf mountains, which the government has charged is the first step toward partitioning Lebanon.
Generally, progress has moved at a snail's pace, despite intense negotiations behind the scenes by the government of President Amin Gemayel and the Saudi-designated Lebanese negotiator, Rafik Hariri, who has been moving around Lebanon to meet with rivals in their respective strongholds.
''It is a race against time,'' commented a Western envoy, reflecting concern that events on the ground might, once again, overtake mediation efforts.
The dangers were reflected in the thundering explosions that echoed through the capital Monday and early Tuesday, shattering the uneasy calm. An official communique said the Lebanese Army and Shiite Muslim gunmen exchanged heavy fire in five suburbs in the largest and longest sustained violation of the truce.
Officials specified, however, that the militiamen were not members of ''Amal, '' the largest Shiite organization that has had previous clashes with the Army. Rather they said they belonged to a smaller, unnamed Shiite splinter group. This could mean that yet another group has joined the already multifactional fighting.
The renewed fighting broke out, at least in part, because the four-man military committee - composed of Lebanese Army, Druze, Amal, and Christian Phalange representatives - has made little headway beyond reopening the Beirut airport and the southern coastal highway. Discussions have also centered on exchange of prisoners held by the rival militias and relief aid for refugees. But there has been no agreement on the pivotal issue of how the cease-fire can be monitored and enforced.
The government and the Phalange have backed the use of United Nations troops. This has been rejected by the two other factions and Syria. Damascus reportedly favors a new Arab force for deployment in the Shouf. That would be the third peacekeeping body in Lebanon. There is already a 6,000-man United Nations force in the south as well as a 5,200-member multinational force in Beirut.
There is also acrimony at the political level about the means of reconciliation to end eight years of war. Officials have admitted they are ''stymied'' by conflicting proposals for the place, time, and format of talks. Because of a series of previous assassination attempts on several of the 12 men scheduled to participate, there are security concerns about a Lebanese venue.
The atmosphere of reconciliation was also impaired by the announcement over the weekend by Mr. Jumblatt of a new civil administration to provide public facilities and look over day-to-day life in the Shouf, where there is virtually no government as a result of the three-week ''war of the mountains.''
The pro-government daily Al-Anwar reflected official reaction by labeling the move the ''usurption of legitimate authority,'' adding that it ''renders the call for a national dialogue ineffective, because one of the parties concerned has made his decision without dialogue or agreement with others.''
And a senior official of the Phalange ''Lebanese Forces'' militia charged that this would allow Jumblatt's Syrian and Soviet backers to establish a toehold in Lebanon. He also pledged: ''We'll fight it.''
But the Druzes and Muslims countered that that Phalange and the Christian-led government have overreacted, and are using the step as a means of blaming the Muslims for the delay in negotiations.