For those with enough money or guns, the now 19-day-old blockade is a bust. Champagne and Cuban cigars are among the luxuries that can still be purchased.

But for the poor and those without armed protectors, the Israeli noose around West Beirut creates major hardships. Short of cash, without friends or access to private, public or international relief activities the poor are often ill equipped to fend for themselves.

Even so, no one seems to be starving.

In theory, the blockade seeks to deprive the predominantly western sector of the capital of everything except flour, rice and medical supplies.

Israeli soldiers dutifully confiscate tomatoes or bananas carried back into West Beirut by pedestrians. The troops regularly check diplomatic car trunks, despite protests from diplomats accustomed to protection from such searches.

In practice, the Lebanese have once again outflanked their conquerors. Their legendary business sense and in some cases venality has enabled them to evade stern instructions issued by the Israeli high command.

Examples:

In theory only diplomatic, government and Lebanese Army vehicles are allowed to enter West Beirut. In practice, a 100 Lebanese pound bribe--worth roughly $20--slipped to an Israeli soldier at the national museum checkpoint dividing the city will frequently insure safe passage back into the besieged sector, or back out to safety.

With every passing day the blockade becomes more porous.

Gasoline, which was selling for $35 a five-gallon jerry can two weeks ago, is now going for $15 and is readily available at many a street corner thanks to enterprising Lebanese.

There's one major hitch--that legendary Lebanese greed has prompted some operators to mix in fuel oil with the gasoline and the mixture has caused motors to cough and sputter.

Tomatoes, eggs, eggplants, peaches, cherries, cucumbers, onions, apples, lettuce, mint are to be found in more than adequate supply in West Beirut markets today. Prices, which zoomed to three or four times the normal right after the blockade began on July 3, have now come back down.

Meat, however, remains expensive. Mutton, the Lebanese favorite, is selling at almost twice the $3.20 a pound pre-blockade price largely because the animals must be smuggled on foot through the lines and slaughtered in front of neighborhood butcher shops.

THE PALESTINIANS long ago laid in supplies of food, water and gasoline with this kind of siege in mind.

Even Lebanese, hardened after more than seven years of violence, long since have stocked their larders with canned food and staples.

But, after Prime Minister Shafiq Wazzan's protestations about what he called the "famine blockade," U.S. special envoy Philip C. Habib and President Reagan brought pressure to bear on Israeli Prime Minister Menachem Begin to ease the economic stranglehold.

Until last Friday the International Committee of the Red Cross was being allowed to bring in flour, powdered milk, sugar, dry beans, cooking oil, soap and basic kitchen utensils for displaced families. Suddenly, the Israelis cut this off, apparently on instructions from the Israeli Cabinet.

Then this Tuesday the Israelis agreed to allow 185 tons a day of rice and flour in, but still refused entry to the fuel oil for the bakeries.

Bottles of cooking gas, used in most Lebanese homes, are also in short supply and are now selling at twice their pre-blockade prices.

Merchants throughout Lebanon complain that the invaders are also showing a good bit of their own legendary business sense in blockade conditions, flooding the country with Israeli products ranging from manufactured goods to watermelons.

Despite the blockade, apples, long a major Lebanese export, have been seen on sale in boxes with Hebrew lettering near a Palestinian refugee camp.

DAVID DODGE'S abduction the other day from the campus of the American University of Beirut his missionary grandfather helped found in 1866 was yet another act of incivility marking Lebanon's decline as the Arab world's intellectual capital.

Dodge, the acting president of the Middle East's most prestigious institution of higher learning, is a most dedicated and decent man. It is conceivable that he was kidnaped because his abductors considered him the most prominent American left in besieged West Beirut, in itself a commentary on local mores and on waning U.S. influence here.

Symbolism, even in kidnaping, passes for a fine art in Lebanon. Often, abductions of persons of Dodge's distinction suggest that the abductors want ultimately to trade their hostage for another kidnap victim of similarly august rank. In this case, the most likely candidate is said to be Mohsein Mousavi, the Iranian charge d'affaires who was kidnaped July 4. His associates claim he was last seen at a Phalange checkpoint on the coastal road in the northern part of the country. The Phalange have denied any involvement.

Still, the American University of Beirut once was a byword for tolerance and cultural freedom and diversity in a part of the world increasingly given over to intolerance, religious certainties and intellectual conformity.

In recent years, a dean was shot to death by a dissatisfied former student on the campus and a controversial administrator was similarly disposed of while jogging along the once elegant seafront drive just below the calm and well-kept university grounds overlooking the bay.

Beyond the fate of the well-liked Dodge lies the other side of the disorder of West Beirut that the Israelis have depicted as part den of thieves, part center of international terrorism.

It is more complex, and interesting, than that. Dozens of publishing houses flourished among the ruins, bringing into the Arab world works that many Arab governments would never allow to be printed locally.

This is an honorable Beirut tradition, stretching back more than a century when the Lebanese contributed so much to the Arab cultural and political renaissance.

That taste for diversity is now threatened as never before. In 1976, when the Syrians besieged West Beirut before finally occupying it under the guise of Arab League gendarmes, Beirut's once lively newspapers suddenly lost their bite.

But publishing escaped the Syrians' control as did theater, painting and the other arts.

In East Beirut, Bashir Gemayel's rightist Christian Phalangist militia has brought a form of law and order that many Lebanese in more lawless parts of the country envied.

But not even his most enthusiastic supporters would claim that his muscular brand of Christianity has produced much of a cultural renaissance.

Since the Israeli invasion West Beirut intellectuals complain friends in the east have stopped even telephoning them, as if signifying they consider West Beirut's fate sealed.