ALGIERS, Algeria, Jan. 31--Beleaguered French insurgents, ranks thinned by the desertion of some territorial troops, clung grimly to their barricades in the streets of Algiers tonight. Around them was a ring of tough French army soldiers. Firm army action brought the first cracks in the position of the right-wing dissidents who have been defying the government of President Charles de Gaulle a week.

Army Keeps Out Mob for First Time

For the first time the army cordon around the insurgent stronghold in the heart of Algiers kept out the Algiers mob and most of the rebels' outside support. The marked stiffening of the army's attitude followed the sudden replacement of Brig. Gen. Jean Gracieux by Brig. Gen. Kleber Toulouse as on-the-spot commander. Gracieux was sent back to the countryside to fight the Algerian nationalist rebels.

No assault on the barricades was expected tonight but it was obvious that the insurgents were wavering in the face of the army's successes.

Inside the rebel strongholds, some of the estimated 2,000 holdouts pleaded with one of their leaders, Pierre Lagaillarde, to surrender before it was too late. Others shouted not to give up--that there was still hope.

Army cordons held against the seething crowds of Europeans who tried to get through the main plaza in front of the barricades. Only scattered groups got through out of the estimated 50,000 who tried.

Terrorist Bomb

Not even a terrorist bomb which killed four soldiers flustered the disciplined troops cordons. The bomb exploded on a side street near the barricades.

Top army leaders in Algeria have pledged their suport to De Gaulle since then and general strikes and disorders in other parts of Algeria have subsided. About 300 French territorials, the backbone of the insurgent forces, marched out of the barricades late this afternoon.

One officer at the head of the formation of haggard reservists said the men behind the barricades were now mainly members of the civilian-military organizations led by Lagaillarde and Joseph Ortiz, a cafe owner.

A Lagaillarde helicopter, which dropped leaflets over central Algiers this afternoon, was perched atop one of the university buildings.

As the eighth night of the insurrection settled over the city the crowds dwindled off home and the curfew was being largely followed for the first time since the troubles started.

The troops were thick in the downtown area around the barricades where the insurgents on sentinel duty peered watchfully over the parapets.

WASHINGTON, Jan. 31--Secretary of Defense Thomas S. Gates Jr. said today the Russians probably will have "moderately more" missiles in production and operation than the United States until this country begins catching up in 1962.

But Gates said the intercontinental-range missile gap, about which Democrats in Congress have been protesting, is being offset in other ways.