Long little more than a sleepy cliffside border post, this coastal crossing point between Israel and Lebanon has suddenly become busy handling civilian truck and car traffic.

Every day, hundreds of Lebanese tourists, businessmen and smugglers are now traveling into Israel under the new Israeli "open border" policy which came into effect Nov. 20. Also crossing are 40 to 60 trucks a day, according to border officials.

It is all part of the Israeli campaign to foster a state of "normal" relations with Lebanon against the consent of the Lebanese central government but with the connivance of many individual Lebanese, particularly businessmen and traders.

While an estimated 500 to 600 Lebanese are crossing the border both ways each day, few Israelis are coming to Lebanon because the government has placed a ban on tourist travel due to the uncertain security situation. But Israeli truck drivers and merchants are free to cross and are doing so.

Lebanese were already passing through Israel last summer to use the Tel Aviv international airport after the war closed the one in Beirut. The Israeli airline, El Al, even opened an office in Sidon to facilitate their travel.

But the Israeli government has now taken steps to make it easy for the Lebanese to drive their own cars and trucks into Israel on eight-day visas, charging them $4 a trip. It is issuing car insurance at the border post here. There is also a new branch of Israel's Hapoalim Bank on the Lebanese side of the border.

Visas are still being issued at the Israeli Army headquarters in Sidon, but when a new $160,000 immigration and customs office is completed here shortly, they will become available here.

Police Capt. Alex Benjamin, who has ruled over the border post alone for 26 years, is expecting eight additional assistants to the four already added to help him deal with the anticipated increase in traffic.

Israeli newspapers said 5,000 Lebanese took advantage of the new policy during the first week. Lt. Col. Aaron Gonen, Israeli Army spokesman in Sidon, said roughly 1,000 Lebanese businessmen and traders had visited Israel out of a total of 16,000 civilian visitors from Lebanon since June 6.

One of the main purposes of the open border policy is to promote trade between the two countries even if the central Lebanese government is against this. So far, however, it is mostly one-way trading, with Israeli companies flooding the Lebanese market with fruits, vegetables, olive oil, candy and a wide variety of building and raw materials.

Gonen estimates that Israel's total trade with Lebanon is now averaging $20 million a month, close to 10 percent of Lebanon's estimated total 1981 imports of $2.6 billion. That would mean Israel already is a leading trading partner.

Lebanese businessmen and smugglers are also taking advantage of Haifa port to bring in their goods from abroad duty-free. One importer of electronic equipment getting a license from a special Israeli trade office in Sidon said this had allowed him to save 12 percent overall on import costs, mostly because he did not have to pay the 35 percent duty charged at Beirut port.

The use of Haifa as a free port is one additional reason the Lebanese government is having difficulty raising revenues. Out of an anticipated $500 million in customs revenues this year, less than $60 million had been collected as of September.