EGYPT PUTS STAMP ON SINAI

Swathed in a white kaffiyeh, or headdress, a Bedouin teen-ager named Said leans against a post in Neviot, an Israeli settlement in Sinai 43 miles south of Eilat.

''When do you have to go away?'' he asks his Israeli friend intently.

''By the end of the month,'' replies the Israeli.

''And you can't come back?'' persists the teen-ager, trying to put together the fragments of a complicated story.

''What? And pay $20 just to come from Eilat to Neviot?'' snorts the Israeli. And he walks away in disgust, leaving the boy to puzzle this one out on his own.

The last piece of the Sinai Peninsula, including Neviot, is scheduled to revert to Egyptian control by midnight April 25. Israel is on the brink of the final segment of its phased Sinai withdrawal under the Egyptian-Israeli peace treaty.

The dark, twisted hulks of old tanks and rusting vehicles litter the sands of the peninsula, silent testimonials to the 30 years of war between Egypt and Israel. Land mines scattered throughout the empty plains still occasionally blast Bedouins' goats to pieces if they inadvertantly tread on one.

But after 15 years of Israeli occupation, Sinai is returning to Egypt much changed.

Before 1967 Sinai was Egypt's neglected child, its forgotten population of Bedouin nomads wandering through the desolate landscape as two implacable enemies used its inhospitable wastes as a battleground.

Now the Sinai has become Egypt's darling. The focus of Egyptian national attention for the last decade and a half -- through intensive preparations for war and years of negotiations that led to the Camp David peace accords and Sinai's gradual return to Egypt - the barren peninsula has become a key symbol of national pride.

With the nationwide festivities planned for April 25 also comes an Egyptian desire to imprint indelibly its own stamp on Sinai and make the territory unmistakably Egyptian.

The areas already under Egyptian control are humming with activity. Roads are being leveled, water pumping stations and electric grids erected, and hundreds of miles of pipelines are being laid across the desert.

El Arish, the capital of the northern Sinai governorate, is a boom town. New houses are going up on nearly every street, and new suburbs are being added to the east and west of town. Hotels and holiday cabins are springing up on the beachfront amid the stately rows of palm trees.

In El Tur, the capital of the southern governorate, Egyptian contractors are creating an entire town of gleaming white stone, complete with housing, shops, schools, cafes, and cinemas, to replace the cluster of rundown mud and plaster houses that formed the old settlement.

The ferries across the Suez Canal are strained to bursting with the heavy traffic going to and through Sinai.

''Before 1967,'' says Dr. Ali Abou Zeid, director of the Sinai Development Authority, ''there was always war in Sinai. We didn't want to invest in a place that would be ruined. Now the people feel the real intention of the government to do something.''

The Sinai Peninsula is 21,000 square miles of arid wilderness, strategically wedged between the continents of Asia and Africa. Since Pharaonical times it has served as a bridge for armies headed for the rich land of the Fertile Crescent and Persia - or conversely, to Africa.

The coastal strip of northern Sinai is sandy terrain and marshland. Most of Sinai's settled population and agricultural potential lie here, especially in the area between El Arish and Rafah scheduled to be returned to Egypt April 25.

The Wadi El Arish or El Arish watershed extends down into central Sinai, a region of rolling yellowish-brown hills and gullies and two massive mountain ranges passable only through two strategic passes, the Mitla and Giddi.

Southern Sinai is a region of richly draped, pink granite mountains with plunging wadis and river beds. Off its shores and at the southern point of Sharm el Sheikh and Ras Muhammad, lie some of the world's most magnificent coral reefs. In waters to the west are rich petroleum reserves.

Israel estimates that it has spent $7 billion in infrastructure development and oil drilling in the Sinai since 1967, and much more to build important airfields and military installations. During the occupation Israel also established 12 agricultural villages and the town of Yamit on the northern Mediterranean coast, and two holiday villages and the town of Ophira on the eastern coast.

Egypt has paid a reported $143 million for Israeli-built Sinai installations and plans to expand projects begun there.

The Egyptian government's initial short-term plan for Sinai development, beginning in November 1979 with the first of the six phased withdrawals that have already taken place, has emphasized rapid initial development of infrastruture and housing. It is to be followed by longer-term development of industry and resources.

Egypt is building and repairing 404 miles of roads throughout Sinai. The northern road to El Arish is being widened and resurfaced, with new stone embankments to prevent the encroachment of sand dunes. The gleaming new $30 million Ahmed Hamdy tunnel, 10 miles north of Suez, forms a land link between Egypt and Sinai under the Suez Canal and will be opened officially on April 25.

One top priority is to increase the region's scant water supply. A pipeline to bring potable water 96 miles east to El Arish has reached halfway -- to the town of Bir el Abd -- and will begin supplying water on June 30. The pipeline is scheduled to reach El Arish in 1984. Two siphons under the canal at Ismailia and Deversoir and pipelines in the Ahmed Hamdy tunnel bring irrigation water to Sinai.

Pipelines and booster stations are under construction to convey the water to cultivable areas for land reclamation projects. New wells are being drilled, and studies of underground water are under way.

Electricity from a new 15-megawatt power plant in El Arish is ready to be delivered as far as Rafah on the day of Israeli withdrawal. In southern Sinai electric power lines are being extended from a new steam-powered thermal electric power plant in Suez to supplement electricity from the small generators in the towns on the western coast. Eventually lines from the high dam will be added.

The area's major airstrips are being enlarged to accommodate international flights, and a new port is being built at El Arish by the Suez Canal Harbor Works Company.

El Arish, Sinai's largest town with some 70,000 inhabitants, has already completed several hundred new housing units for summer vacationers, residents, and government employees. Hundreds more are under way.

In El Tur, some local inhabitants have already moved into a spanking new fishermen's village. The windswept coastal town, with its view of giant offshore oil derricks, looks like a huge construction camp, as the giant Egyptian contracting firm of Osman Ahmed Osman & Co. builds it from ground up.

In the smaller towns in the area, administrative buildings and housing for the Bedouins are being constructed.

Egypt is reluctant to have the Sinai population, formerly integrated into the Israeli economy, look to Israel for future employment.

''After El Arish came back in 1979,'' says northern Sinai Gov. Youssef Sabry Abu Taleb, a retired major general, ''at first unemployment rose. We caught many people sneaking back into Israel to work, until we found new opportunities. They were in construction.''

As Egypt absorbs the remainder of Sinai this month, it must also find employment in the north alone for as many as 3,000 individuals who now work in Israel, where salaries are higher than average Egyptian wages. General Abu Taleb says contractors are poised to begin construction work immediately in the eastern zone once withdrawal is completed.

''The matter is not that we don't want them to work in Israel,'' General Abu Taleb offers as the explanation, ''but that it is not natural. We have the opportunities for them to work here, and we want them.

''Creating productive enterprises in Sinai is crucial to the area's long-term employment prospects -- and for the central government's ambitious plans to boost the region's population from 200,000 to more than 500,000 by the year 2000 .

Areas in which Egypt plans development include:

* Tourism. Egypt is eager to continue expanding the lucrative tourist trade. Sinai has become a popular vacation spot for Israelis and other foreign tourists. It is famous for its stark beauty, wildlife, historical sites, and clean beaches.

Egypt has purchased existing Israeli hotels near St. Catherine's Monastery and the site of the biblical Mt. Sinai and at Sharm el Sheikh, Dahab, and Nuweiba on the east coast. A new 150-room Marriott hotel is nearing completion in El Arish, and a multitude of holiday cabins and summer apartments are being built in anticipation that the northern coast, with its white sand beaches and palm groves, will become a major resort area. The Israeli settlement of Yamit, say Egyptian tourism officials, will become a holiday village.

Two new hotels are being constructed in the St. Catherine's area; on the western coast, hotels and cabins are planned for Ras el Sudr, Abu Rudeis, Ras Misalla, and El Tur.

The old Nefertiti airline that handled Egyptian-Israeli flights is being transformed into a new company called Sinai Air. It will have flights to Tel Aviv and different points in Sinai several times a week, sharing the tourist traffic with Arkia, an Israeli airline.

Egypt has agreed to grant Israelis and other foreign tourists on-the-spot, special, 48-hour Sinai visas from an Egyptian consulate to be opened in Eilat. Israelis and others will be allowed to drive their cars as far as Sharm el Sheikh and St. Catherine's. For longer stays or trips to Cairo, Israelis and others will be required to get a regular Egyptian tourist visa. Permanent border-crossing points in Sinai will be opened at Rafah, El Ouga, Ras el Naqab, and Taba.

* Petroleum. The 1975 Sinai disengagement agreement returned the Abu Rudeis oilfields in southwest Sinai to Egyptian control, and in September 1979 Israel handed over the Alma oilfields (now called the Shuab Ali fields) it had developed. Egypt has expanded production at the Abu Rudeis and nearby Belayim fields from 70,000 to 130,000 barrels a day. By 1986, production could reach 180,000 barrels a day.

The Shuab Ali fields are being rehabilitated after having apparently been overexploited by Israel. Promising new geological structures have been found adjacent to the existing fields.

Eighty percent of Egypt's daily production of 700,000 barrels of oil comes from the Gulf of Suez. Peace and the withdrawal have given Egypt access to the formerly restricted eastern half of the gulf for expanded oil exploration.

Several oil companies are also conducting explorations off the northern Sinai coast, and Egyptian Oil Ministry officials say the preliminary findings from test wells look promising.

Egypt has negotiated an agreement with Israel to sell the Jewish state 2 million tons of oil a year.

* Mining. Geological surveys have shown the presence of coal, manganese, gypsum, copper, phosphate, sulfur, and turquoise in Sinai. The question now is which mineral deposits can be commercially exploited.

* Local industry and agriculture. The $2.5 million US aid study by the American consulting firm Dames & Moore on resource development in Sinai has recommended establishing industrial zones in the El Arish and east Qantara areas. It recommended a variety of small industries that could be quickly and profitably developed, including cottage textiles, leather tanning, fish and date processing, salt and sodium bicarbonate factories.

Lake Bardawil, a 164,000-acre lagoon on the northern coast, is a rich fishing ground and bird sanctuary. Fishermen from the south also fish in the Red Sea.

The study pointed out the high costs of large-scale land reclamation in the region. Nonetheless, the Egyptian government, concerned about the growing gap between Egypt's population and its food supply, has begun agricultural projects in nearly all the settled areas. It also has ambitious plans to expand cultivable land in the area between El Arish and Rafah -- where the rainfall is heaviest -- and in southern Sinai, using the Nile water pipelines and underground wells.

One of the issues that has gained international attention during the withdrawal period is conserving fragile coral reefs and the area's rare animals and birdlife.

Although Egypt has strict environmental laws, they are not often enforced. The governors of northern and southern Sinai have pledged strict enforcement of environmental laws through their local police force, and the Ministry of Tourism says an interministerial committee is being formed to review conservation measures -- not only for the Sinai, but also in the Red Sea region -- and create national marine parks in the coral reef areas and in the interior.

According to the peace treaty, Egypt is allowed only a limited military presence in areas that have been given back so far -- and in the eastern zone to be evacuated on April 25, only a local police force. The 2,500-man multinational force and observers based near Rafah in the north and Sharm el Sheikh in the south will carry on periodic inspections to guard against a military buildup on either side.

Just as important, Egypt's big development push -- the planting of fruit trees that take years to mature, the building of sports stadiums, hotels, and low-cost housing -- should act as another powerful deterrent to hostile action.

''Am I building all this in order to destroy it?'' asked Muhammad Momtasel, chief engineer for the Sinai Development Authority at El Arish, pointing to the clusters of pastel housing blocks rising out of the sand.

Prickly Egyptian pride -- the karama, or honor, they felt they had lost in the 1967 defeat -- is being restored.