The drab scarfs and conservative dress that only recently became common for women here are being replaced by full black body drapes, or chadors. New posters plastered on buildings boast of the coming ''Islamic revolution.'' Black banners, strung across boulevards and alleys and wrapped around statues and mosques, call for people to ''sacrifice with your life and your blood.''
Lebanon is experiencing a rise of Shia Islam - a Muslim consciousness that borders on the kind of revolutionary zeal so far witnessed only in Iran.
A mere two years ago the various Shiite groups were background players in the Lebanese trauma. Now, they are at center stage.
The 10-day Shiite religious festival of Ashoura, which ends today, has made the trend highly visible: the parades of covered women and children hoisting large portraits of their ''martyred'' menfolk, the nightly rallies and speeches advocating stricter adherence to the faith, the rhetoric of the somber street decorations, and the attacks on places that sell alcohol.
Coming shortly after the Sept. 20 bombing of the US Embassy annex, for which Shiite extremists are the prime suspects, the manifestations have heightened sectarian sensitivities - and fears.
Although by far the largest Lebanese sect, the Shiites have only recently begun to challenge the Maronite Christians and Sunni Muslims for prominence - politically, socially, and militarily.
And now, a new strain of Shiite militancy has cast doubts on hopes for national reconciliation in Lebanon.
Until this year, the majority of Shiites followed the leadership of Nabih Berri, the moderate chief of the Amal (''hope'' in Arabic) party. But over the past few months, the fundamentalist Hizbullah, or ''Party of God,'' has gained a foothold in Beirut and begun to threaten Amal and Mr. Berri's commitment to help rebuild a nation for both Christians and Muslims.
''We are an Islamic revolution. Hizbullah talks to the people about the real Islamic religion. Iran was a big influence on us,'' explains a young bearded cadre of Hizbullah whose nom de guerre is ''Hamze'' (not to be confused with the Amal military commander by the same name).
''Our slogan is 'death to America in the Islamic world'.... We are going to strike the US as long as our people continue to be killed in the (Israeli-occupied) south,'' he said with the enthusiastic agreement of several other Hizbullah members.
But he denied knowledge about the annex bombing or the group Islamic Jihad, saying only that ''a good Muslim'' was responsible for the attack. He added, ''The fire of Islam will burn the US like it is burning Israel.... Our goal is to die for Islam. We love to die for Islam, like the kamikazes.''
Amal is deeply concerned about the new movement. ''They want a 100 percent Islamic state which we believe impossible,'' said Amal's deputy leader, Col. Akef Haidar. ''Amal is an Islamic movement, but like our prophet we tolerate other (religious) communities. We want a real democracy where all people have rights.''
Colonel Haidar conceded that the fundamentalist pull has hurt Amal. ''Berri is losing on the ground. Things are going badly with the new government,'' in which Mr. Berri is a cabinet minister.
''Hizbullah is becoming stronger and stronger. We are expecting Hizbullah to grow because we are too moderate as a movement,'' Haidar said.
And he went as far as to predict that, without significant reforms that give majority Muslims a greater say in the government dominated by minority Christians, Hizbullah and other extremists would eventually gain the upper hand. ''Hizbullah is waiting to take over when others fail,'' he said.
Originally sponsored by Iran's paramilitary Revolutionary Guards, who were dispatched to eastern Lebanon during the 1982 Israeli invasion, Hizbullah has mushroomed.
Over the past two years it has grown from a small core of radical clerics and students based in Baalbek in eastern Lebanon to a major movement with branches in Beirut and south Lebanon. Many of the militant expressions of Ashoura, the change in dress codes, attacks on bars, and the threatening banners are considered the direct result of Hizbullah's growing influence.
Yet little is known about the movement, including the identity of its leaders.
''Khomeini is our big chief,'' said Hamze, referring to the Iranian leader. ''He gives the orders to our chiefs, who give them to us. We don't have a precise chief, but a committee.''
Colonel Haidar explained: ''There is no Hizbullah in the sense of a political party with some organization or structure.'' He claimed not to know its chief organizers, but estimated that there were roughly 5,000 Hizbullah fighters in Beirut.
Colonel Haidar and Hamze both said that Hizbullah has absorbed several Shiite groups, such as the militant Islamic Amal, Al Dawa (''The Call''), Jundallah (''Soldiers of God'), and the Islamic Students Union. ''Hizbullah is not one party but four or five, a kind of Islamic front, very rigid and very strong,'' Colonel Haidar commented.
''There is not an open system of recruitment,'' said Fuad Khouri, a Shiite expert at American University of Beirut. ''That's part of the mystery. You volunteer for it. Membership is fluid. You are in it and not in it.''
''Every good Muslim is a member of Hizbullah,'' said Abdullah, a Hizbullah member and organizer of an Ashoura parade of children in the west Beirut suburb of Bir Abid.
''When a man believes in God, he is a member. There are no cards.''
Reflecting the movement's militancy, he added: ''The future is for the Muslims. The Soviet Union and the US want to take over the earth. With Imam Khomeini, we can succeed to take these forces out, to destroy these forces.''
''The birth of Hizbullah in Lebanon is part of the overall Islamic challange, '' said Sheikh Mohammed Hussein Fadlallah, a Shiite cleric who regularly denies reports that he is a leader of the movement, while admitting his teachings have been a major influence.
The most popular of his many books, ''Islam and the Logic of Force,'' can be found throughout the Arab world.
''The new Islamic generation,'' he said, ''has now begun to carry Islam far from the traditions which held that Islam was just as a way of knowledge. Hizbullah is an organization born from Islamic concepts that are trying to face political reality.''
Sheikh Fadlallah has condemned the three attacks on American targets over the past 18 months.
This summer he went on nationwide television to urge that foreigners not be kidnapped or harassed. And at a Hizbullah rally for Ashoura this week, at which he was the main speaker, he appealed for moderation and tolerance.
At the same time, Fadlallah said in a recent interview, ''when it is necessary I approve of violence. Every person needs to defend himself. If a man needs to use violent ways, he must use it.''