The Lebanese government is becoming increasingly alarmed about Israeli activities in the southern part of this country that it says includes the establishment of a permanent military presence and land seizures that amount to "the annexation of Lebanese territory."

These charges, contained in a letter sent this week to the U.N. Security Council, are part of a Lebanese campaign to alert international opinion to what they are convinced is a carefully devised Israeli plan to take advantage of the distractions of the Iranian-Iraqi war and the U.S. presidential election to consolidate its hold on the south.

Among other things, Lebanon is pressing for a revival of the Lebanese-Israeli armistice commission, established in 1949 at the end of the first Arab-Israeli war, as a way of obtaining a renewed commitment by Israel to honoring the existing border. So far, Tel Aviv has rebuffed the Lebanese request.

Lebanese Foreign Minister Fuad Boutros and President Elias Sarkis both met this week with U.S. Ambassador John Gunther Dean about the situation in the south before he left for consultations in Washington. Press reports said they discussed the Lebanese demand for reactivation of the commission.

Lebanon's renewed anxiety about Israel's intentions in the south comes amid a series of Israeli air and ground attacks on Palestinian guerrilla positions as far north as the outskirts of Beirut, which Lebanon and the Palestine Liberation Organization regard as harbingers of a full-scale Israeli offensive into this war-ravaged and bitterly divided country.

It also follows a petition to the Lebanese government from villagers in Adayeseh, inside the strip of border territory controlled by a breakaway Lebanese Christian Army officer, Maj. Saad Haddad, complaining that the Israelis have seized about 450 acres of their land and offered them compensation for it.

This incident, while not the first of its kind, has aroused new Lebanese concern about Israeli designs on the border region since it fits into a pattern of small land seizures by Israel during the last six months or so.

U.N. officials here at this tiny isolated enclave within Haddad's larger Christian enclave confirm that Israel is involved in activities along the border, which they describe officially as "permanent border violations" rather than "annexation."

U.N. officials are having increasing difficulty verifying these violations, however, because Haddad is challenging their movement within his fiefdom and their access to five outposts manned by a U.N. observer group since the 1949 armistice. Haddad wants resupply of the four-man outposts cut from five times weekly to twice, with these only under escort by his militia.

The headquarters for the observer group and the U.N. Interim Force in Lebanon (UNIFIL) is here at Naqoura, a village surrounded by hostile Haddad forces except for a coastal road link to Israel 1 1/2 miles away.

It is perched on a bluff overlooking the sea and dominated by hills from which Haddad's militia have twice shelled the unprotected U.N. buildings. In the last attack in April, four helicopters were destroyed and 13 buildings hit by mortar shells. Since then the United Nations has built a dirt rampart to protect the landing pad and hospital, brought in a French paratroop unit with heavy armored vehicles for defense, and moved its operations center to a better protected spot.

Basically, however, the United Nations relies on a combination of international pressure and Israeli sufferance to stay in this precarious coastal base.

U.N. officials say Israeli activities within Haddad's self-proclaimed "Free Lebanon" have become more open and that Israel is pressing Haddad to expand his enclave northward into U.N.-controlled areas.

He now controls about 80 square miles in a curved swath of rugged, mountainous land running from the Mediterranean east and then north to the Litani River, and ranging in width from about one mile to six or seven. U.N. officials estimate that the territory controlled by Haddad contains 80,000 people, 60 percent of them actually Shiite Moslems, and they say Haddad has built up a force of perhaps 2,000 militia and former regular Christian soldiers who were stranded in the south during the 1975-76 civil war.

A few months ago Israeli soldiers in southern Lebanon began wearing the uniforms and patches of Haddad's militia.

This has made it more difficult to verify who is involved in incidents. For example a U.N. report on a kidnapping from a village within U.N.-controlled territory Thursday said, "Positive identification of the abductors was impossible as most [Israeli] forces wear DFF patches and speak Arabic." U.N. officials refer to Haddad's army as "de facto forces" (DFF).

Israel keeps a permanent daytime force of between 200 and 300 soldiers in Lebanon, but the number goes much higher at night, U.N. officials say, when the Israelis carry out their own patrols and operations throughout Haddad's enclave. They also have their own artillery positions and observation and command posts dotting the southern Lebanese hills as well as a radar station at Hayyadah, five miles inside Lebanon, monitoring Palestinian camps near Tyre, they add.

U.N. officials do not know just what Israel has done at Adayeseh since observers sent to verify Lebanese peasant claims of land "annexation" were turned back by Haddad's forces. But they think the Israelis took the land and fenced it to protect the Misgav Am kibbutz, which was infiltrated by Palestinian commandos in April.

A similar thing happened last spring, they say, south of Alma Ashshab, where Israel built a two-mile road several hundred yards inside Lebanon and then put up an electrified fence to protect Hanita kibbutz nearby.

But such road-and-fence building activity inside Lebanon may not always be to protect kibbutzim, according to U.N. spokesman Timur Goksel.

"We feel they want a chain of domination features to extend their security zone," Goksel said. "They want to control the high areas and dominating zones in our areas, too."