Gunmen are back on the streets of Beirut

The quick, deafening bursts of small explosions have become a regular feature of west Beirut nights again, to the point where many Lebanese do not even bother to look out their windows.

They know that the targets of the blasts are usually nightclubs, the attackers Islamic fundamentalist militias.

In east Beirut a new barracks for Christian militiamen has appeared in a ''front line'' suburb. Sandbag emplacements protect gun-toting guards.

Although the Lebanese capital is technically at peace again, the factions on both sides of the dividing ''green line'' are clearly visible these days, violating the security plan introduced last summer.

The appearance of gunmen on the streets is, in part, the result of the stalemate on political reforms designed to end almost a decade of strife, diplomats say.

''Increased militia presence is at best an unnerving manifestation of the nihilist achievements of the Cabinet,'' Beirut's English-language Daily Star newspaper editorialized earlier this week.

The six-month-old Cabinet of warlords has yet to show even minor progress on evening the balance of power between the Christian minority, which dominates power, and the Muslim majority, which wants more power.

That, in turn, has increased tension and rhetoric. Druze leader Walid Jumblatt said recently that peace was impossible under the regime of President Amin Gemayel.

''It is impossible to have peace when there are fascist parties in power,'' he said. ''I hold that Amin Gemayel represents Lebanese fascist interests. We will try to find solutions, but I have no reason to be optimistic.

After Monday's heated Cabinet debate, Shiite Muslim leader Nabih Berri hinted that he and Mr. Jumblatt might resign because ''the regime's procrastination and stalling on political reforms can no longer be tolerated.''

And Jumblatt reportedly told Mr. Berri during a telephone conversation: ''We are about to take a dangerous decision vis-a-vis the regime's practices.''

But the renewed visibility of arms also reflects developments within the rival religious communities, the Lebanese say. Both sides appear to be moving to consolidate their own power bases.

The Christian Lebanese Forces militia changed leadership last week, installing a man with well-known loyalties to President Gemayel. Fuad Abu Nader, a nephew of Gemayel, was elected to replace Fadi Frem. Dr. Abu Nader's election was important because the ultra-rightist Christians, who had begun contesting Christian policies and trying to take over the militia, were defeated.

Since the death in August of his father - the Christian patriarch and founder of the Phalange Party - President Gemayel has slowly tried to establish hold over the powerful and increasingly independent militia. Abu Nader's election is a start, but military sources suggest the contest is not over.

Christian sources say the hard-liners are still not ready to accept the kind of compromises Gemayel needs for national reconciliation. The Christian extremists may be ready to take up arms against the moderates to avoid what they see as Christian surrender, the sources say.

In the run-up to the election, there were a series of incidents among Christian rivals, including a brief clash in a key Christian town outside Beirut. American diplomats, already restricted from traveling in many Muslim areas, have been discouraged from visiting the Metn area until the situation crystallizes.

Meanwhile, a new Muslim alliance has been formed by six leftist parties. It is headed by Jumblatt. In membership and goals, the new National Democratic Front is reminiscent of the National Salvation Front, which waged a political and military campaign against the Gemayel regime and forced the formation of the new government under Prime Minister Rashid Karami.

At a press conference last week, Jumblatt said one of the new alliance's goals was ''to thwart the (Christian) Phalangist fascist scheme of seeking to impose Phalangist hegemony and domination on the country.''

Notably absent from the coalition is Shiite leader Berri, who has traditionally refused to join Muslim groupings although he supports their political programs.

Berri is also trying to consolidate his hold on the Shiites, by far the largest of Lebanon's sects. His leadership has been challenged by increasingly visible and active fundamentalists, mainly those aligned with the radical Hizbullah (''Party of God''). But so far it appears he has been having difficulties.