Beirut's mayor -- a supreme optimist with dreams of rebuilding the battered ''Paris of the Orient''

Mitri Naamar, mayor of Beirut, may be the world's supreme civic optimist. He has to be, for it is too easy to be pessimistic about Beirut.

''One has to dream to do great things,'' Mr. Naamar says.

What this mayor dreams of is the post-war Beirut. Mr. Naamar sees his woefully battered city reconstructed, decentralized, and once again the sparkling ''Paris of the Orient'' that it was until the Lebanese civil war laid waste to large sections of it beginning in 1975.

''There's always a bright side, even to these current problems,'' Mr. Naamar says. ''Once the situation comes back to normal, the war will have allowed us to reconstruct the city center.''

Mr. Naamar, cheery and cosmopolitan, is an urban architect by profession. Even before the war began in 1975 he had been working toward a redeveloped downtown Beirut. He has, he says, accumulated four tons of proposals and diagrams for rebuilding the city.

''Work before the war was very interesting, but the war changed the atmosphere,'' the mayor says.

There can scarcely be a mayor that has had Mr. Naamar's sort of problems - not even New York City Mayor Ed Koch. Mr. Koch doesn't have a city cut in half, ringed with Israeli tanks, and subject to spectactularly destructive artillery duels. Israelis and right-wing Christians of the Phalange control the eastern part of this city of 1 million. Palestinians and leftist Lebanese control the west. More than 150 armed factions roam the neighborhood streets with automatic rifles, extorting local residents and Balkanizing the city. Sniper lines cut through the city center.

For more than two weeks, the Palestinian-Lebanese side of the city has been progressively choked by a blockade of, at times, food, water, electricity, and people. Garbage has piled up on the west side. This is the longest time in the past seven years that city services have been interrupted, but even now municipal workers are braving the firefights to try to patch up the ever-increasing damage.

Mayor Naamar (his actual title is administrator of Beirut, an appointed post he assumed in 1977) has had to maintain offices in six locations throughout the city. When one area gets particularly violent he and his staff work out of another. He spoke to the Monitor last week in his modern, comfortable east Beirut office.

In its dramatic seaside geography and ethnic diversity, the mayor says, Beirut is like Marseilles. In its reconstruction needs it resembles post-World War II Rotterdam. It cannot be compared to Berlin, he feels, because physical separation has never been quite so complete - although the Israeli-Phalangist blockade has divided the city as never before.

In all the years of civil war, Mr. Naamar says he has not once been in personal danger in the line of duty. This is because, he believes, ''it is known by everybody that the city is working for the welfare of all the people in these trying times.''

Despite the war and the breakdown in law and order, Beirut's municipal tax on construction and commerce continues to finance the bulk of city government. In the first six months of 1982, the mayor says, tax revenues accounted for $150 million to which the central government was adding a small monthly allocation to help with salaries for the 6,500 employees. (The city turns a blind eye to extorted taxes local militias exact.) A pre-war budget surplus and aid from Europe and the United States has helped Beirut cope with conditions during the past seven years.

In his optimism, Mr. Naamar sees certain of the changes wrought by the war as having beneficial effects. These include the reestablishment of businesses away from downtown and the forced demolition and abandonment of the old city center and the souks (markets). His plan for redeveloping the center of the city calls for reconstruction of public buildings and restoration of the souk to its original Ottoman appearance. Also planned are a subway system and a new arterial street system.

Costs of reconstruction, which was to begin in 1978 when an extended lull seemed to indicate the civil war was over, have escalated from $3 billion to $7 billion. Mayor Naamar says, however, that finances are not a great concern. One-third of the cost will be covered by the government and two-thirds by private enterprise. A $500 million starting fund already has been established.

''In spite of the war, the economic and financial structures in Beirut are acceptable,'' the mayor says. ''One thing one cannot destroy is the Lebanese brain or spirit. The Lebanese are always ready to pour money back into Lebanon.''