Beirut — The telltale signs are everywhere: ongoing sales in shops of all goods at 50 percent discounts or more; old cars parked on posh streets by families who once prided themselves on acquiring a new Mercedes or BMW each year; big gaps on grocery shelves once reserved for luxury imported foods; open talk in the business community about banks in trouble.
As a new United States State Department survey confirms, Lebanon's economy and its traditionally resilient banking system have joined the long list of victims of the nation's decade of violence. Among the hard facts comparing the general decline in 1983 with the previous year:
* The value of the Lebanese pound has depreciated by 50 percent.
* Exports declined by more than 50 percent.
* Industrial production, already hard hit, dropped by another 30 percent.
* For the first time in three decades, Lebanon went from a surplus in its balance of payments to a deficit, estimated now at $1 billion.
* Badly needed aid from oil-rich Gulf states, pledged in 1979, dried up.
* Remittances from Lebanese who fled abroad because of hostilities were halved. Those emigrants had comprised one-third of the country's labor force.
* Whole sections of the country were cut off by occupying foreign armies, diverting vast sums from agriculture and transportion revenues.
This situation represents a dramatic change from the sometimes stunning prosperity that marked the era of the 1975-76 civil war and the sporadically violent aftermath. Banks in particular thrived, despite the ravaging of Beirut's commercial district.
Even during the traumatic 1982 Israeli invasion, banks boomed. An American Express bank review reported a record inflow of deposits during that war, and a few banks actually opened new branches at the height of the siege of the capital.
But the past six months have marked a turning point. As the State Department survey concludes: ''The Lebanese are . . . deeply pessimistic about their own and their country's chances for political and economic survival. In a country which has prided itself in the past 10 years on being able to cope with any setback, this deep despair is a significant change.''
Banking activity was down by at least 30 percent last year, according to a Lebanese economist, with up to a dozen of the country's 91 banks in trouble. Arab investment in particular has shifted from Beirut to Bahrain and European banks.
Because of the current limited number of safe investment opportunities in Lebanon, banks have increasingly bought government treasury bills, which now account for up to 40 percent of total local deposits, according to economist Marwan Iskander.
Loans are now primarily for questionable projects, many of which have little chance of prompt repayment because of overall stagnation and additional destruction from recent fighting. ''Banks show rapidly rising loan portfolios, but it has nothing to do with good business,'' said one foreign banker.
Other sections of the private sector have also been hard hit. Real estate, a major indicator of commercial activity, was down 40 percent. In agriculture, food prices on the shelves are up 12 percent even though farmers' prices are down 15 percent. The difference is attributed to such factors as transportation costs, which have soared by 200 percent.
The Israeli Army's presence in southern Lebanon has been a major detriment, according to the State Department. The Israelis frequently close access roads to the rest of the country, which hurts trade.
The Israelis have also attempted to divert sales to their economy by opening markets for their own merchandise, such as food, textiles, appliances, and chemical products. Some $4 million worth of goods from Israel now make their way into Lebanon, although the Israelis forbid Lebanese goods to cross the border.
Meanwhile, the Arab world is also cutting back on its imports from or via Lebanon, due in part to fears of indirectly buying Israeli products and as a result of their own loss in oil revenues. The State Department estimates Lebanon's biggest customer, Saudi Arabia, cut back by almost 13 percent, while the Iraqi market ''virtually disappeared,'' dropping by 83 percent. The Arab bloc traditionally bought 90 percent of Lebanon's exports.
The cost of rebuilding Lebanon's infrastructure over the next decade is now estimated at $18 billion. Pledged Arab aid has been delayed, since the Gulf states do not want to hand over one cent until the Israeli Army has withdrawn. That in turn has delayed the plans of dozens of Western interest groups, industrial consortiums, and multinationals looking to capitalize on development projects. Virtually all of the major reconstruction programs are now on the back burner.
The private sector holds the government responsible. ''The problem is that we have no political leaders with any economic sense,'' said Elias Saba, chairman of Allied Commerical Bank.
Mr. Gemayel's government has its own financial woes. Defense expenditures, the single highest item in the budget, soared as Lebanon tried to rebuild its Army, while at the same time keeping it in bullets for the ongoing battles. The US survey suggests the defense allotment, $685 million, is likely to end up doubling. Social-service costs have also skyrocketed, with another 150,000 people becoming refugees during last autumn's mountain war.
The next year will be a make-or-break situation for Lebanon, according to several bankers and economists. As Mr. Iskander summarized: ''Either in 1984 the political situation settles down and we do receive aid for reconstruction and welfare, and therefore can close part of the deficit in the budget and balance of payments - or we end up with an enormous public debt and inadequate liquid reserves. And then there will be no way to put things right again in Lebanon.''