The Libyan capital's new international airport is open at long last, a gleaming up-to-date facility that should relieve some of the suffering of travelers who had been forced to use one of the dirtiest and most crowded airports in the Arab world.

On a recent flight from Rome, passengers applauded and shouted "praise to Allah" "Bellissima" when they saw that their plane was taxiing up to the terminal instead of the old one.

Inside, they found that the Libyans have done foreigners the favor of allowing arrivals and departures to be posted in English as well as Arabic, a rare exception to the Arabic-only rule that prevails throughout the country. Immigration and customs forms and announcements on the public address system, however, are still exclusively in Arabic.

The bright new surrounding have not softened the stony looks of the immovable Libyan customs agents who accost arriving passengers, on the lookout not only for liquor but also for unauthorized books and periodicals.

Most magazines and newspapers are simply confiscated, regardless of language or content - the Manchester Guardian, the International Herald Tribune, Corriere Della Sera, the Alitalia magazine. This is partly because the governmentnow has a monopoly on the import of these materials.

Books are treated differently. All are taken away, but those that are deemed innocuous can be reclaimed a few days later. Books in Japanese, which hardly anyone in Libya can read, meet the same fate as books in Italian or English are taken away, but those that are

The books that are not returned, those that are politically or religiously suspect, simply disappear. It is not that all Libyans are prohibited from reading them - the library in the Foreign Ministry, for example, contains a useful collection of books that would never be allowed in at the airport, including the memoirs of those two arch-villains, Israeli Prime Minister Menachem Begin and Egyptain President Anwar Sadat.It's just that the government censorship apparatus controls the distribution, which is limited.

THE AIRPORT is only the first indication of the construction boom that is transforming the face of Tripoli. Even two years ago, the town retained some of the charm of its Mediterranean-style arcaded buildings, but now it is a traffic-choked hodgepodge of schools, factories, hospitals, sewers, freeways and high-rise apartment buildings.

It is wholly out of character for Libyans to live in high-rise apartments, but the flow of rural folk into the city has made it necessary.

Unlike Saudi Arabia, Libya is spending little of its oil wealth on fancy offices for government ministries and banks. Priority here goes to productive construction - harbors, factories, communications - and to public service facilities such as schools and housing.

That may be the reason the construction boom has not included a single first-class hotel, of which Tripoli has none though one is planned. Libya has no need of luxury hotels to attract businessmen, since they come anyway in search of lucrative contracts, and the country has no interest in tourism.

With 1,100 miles of unspoiled Mediterranean coastline, magnificent Roman ruins, good weather and proximity to Europe, Libya could be a major tourist center if it wanted, to, but it doesn't.

The Libyan leader, Col. Muammar Qaddafi, and his team consider tourism both demeaning and dangerous, since tourists bring with them liquor, gambling, sexual temptation and unpalatable political notions. And Libya, with all its oil wealth, does not need tourists' money.

Although there are hardly any tourists, there are plenty of visitors, as Libya welcomes a seemingly endless parade of official delegations - students, workers, women's groups, liberation organizations, religious groups - who come here as guests of the government to hear Qaddafi's message of Islam and anticolonialism.

No sooner had a conference of Arab woment left last month than their places were taken by several dozen young men from Uganda, who are here for three months, at Libya's expense, to inspect Libyan industrial projects. They said they found clothing and consumer goods cheap here, more a reflection of shortages and high prices in their own country than of any baragins to be found in Libya.

ONE COUNTRY that has been strangely absent from those that send students and workers and women here is the People's Republic of China.

Libya, one of the most radical of the Arab states, still maintains diplomatic relations with the nationalist Chinese government on Taiwan.

This according to U.S. sources, is largely because of Libyan gratitude and friendships built up with Taiwanese physicians, who have played a significant role in Taiwanese technical advisers who work with the Libyan military.

Thus, here in Tripoli, as in Washington and Jeddah, the flag flying over the Chinese Embassy recently was the red, white and blue gearwheel of the Nationalists. This, however, is expected to change as a result of the recent surprise visit to Peking by Qaddafi's right hand man, Maj. Abdel Salam Jalloud, and the announcement that Peking and Tripoliare establishing diplomatic relations.

The Libyan flag is now solid green. It used to be nearly identical to the red, white and black of neighboring Egypt, but was changed when Sadat went to Jerusalem last year.