Yemen, once known as Arabia Felix, finds oil wealth has passed it by

Geology has favored the east of the Arabian Peninsula; but in the west, no oil flows. That is a sad fact of life for the two countries now sharing historic Yemen. It could yet prove a destabilizing factor for the peninsula as a whole.

For the ancients, Yemen was known as Arabia Felix,m "happy Arabia." The reason: cool, soaring mountains terraced for cultivation; hidden valleys where powerful traders were 500 years ago constructing eight-story skyscraper cities; rich fisheries in two sunny seas.

For successive colonial powers in the region, interest centered on Aden -- a staggering natural harbor commanding the entire northwest corner of the Indian Ocean. For the British, Aden was a vital staging post in imperial communications with India.

But the British largely failed to develop the port's hinterland, and when they pulled out of Aden in 1967 a radical coalition of Yemenis took over and steered South Yemen firmly into the Soviet orbit. The whole sprawling collection of up-to-date port facilities, remote valleys guarding ancient lost civilizations, and spreading desert became austerely known as the People's Democratic Republic of Yemen.

In North Yemen, government had for centuries been in the hands of a traditional religious leader. But Egypt's president Nasser, just up the Red Sea from the Yemens, supported a modernizing republican movement in North Yemen in the early 1960s. Soon thousands of his troops were tied down in remote Yemeni valleys, but their threat was sufficient to prod the Saudis into supporting the religious leader.

Compromise was reached only in the aftermath of the Arabs' defeat in their June 1967 war with Israel: The Egyptians withdrew, and North Yemen emerged as the military-dominated Yemen Arab Republic.

The Two Yemeni states are each today committed to inter-Yemeni unity. But their social and political systems remain fundamentally different.

In the North, successive officers' governments rule only by outwitting all other comers in the traditional Yemeni game of tribal alliances. In the South, determined efforts have been made to halt that game altogether and supplant it with a Soviet-style one-party system.

Such developments are extremely alarming for the Saudis. The Saudi royal house sees itself as leading the fight against communist influence throughout the Mideast and in the Islamic community worldwide. Yet here, on its very borders is one state firmly allied to Moscow, and another continually vacillating between an East-bloc and a West-bloc orientation.

The Saudis have tried at different times either to subvert or to moderate the regime in Aden. But the Soviets appear eager that their allies in South Yemen resist Saudi peace overtures: In 1977, the South Yemeni head of state was overthrown by more staunchly pro-Soviet followers who accused him of negotiating secretly with riyadh.

A further "palace coup" since then has brought the Soviets into even greater control in the Aden of the current youthful leader, Ali Nasser Muhammad Hasani.

The East-bloc presence in South Yemen, estimated by Oman to involve some 4, 000 East-bloc military and technical personnel, is deeply worrying the Saudis. equally disquieting is the continued chronic instability in North Yemen.

Throughout the peninsula, state boundaries have traditionally been fluid. Here in the mountains and valleys of the southwest, there is a constant movement of people and ideas, particularly between the two Yemens, and between North Yemen and Saudi Arabia.

The North Yemenis have long claimed the neighboring Saudi provinces of Najran and Asir as their own. Certainly, physically, they have a lot in common with Yemen. Yemenis can travel to them relatively easily; from there, they fan out to work throughout the labor-hungry Saudi economy.

An estimated million of North Yemen's 6 million citizens are migrant workers, nearly all of them is Saudi Arabia. In 1976-77, the latest year for which figures are available, their annual remittances totaled $842 million -- North Yemen's largest single source of foreign earnings, by far.

those earnings are now trickling into a tentative modernization of the beautiful ancient Yemeni capital of Sana, where graceful mud-brick housing blocks were always pleasantly spaced with fertile and refreshing garden plots.

But rather than going in for long-term development programs, most Yemenis seem content to spend an increasing proportion of thei earnings on qat.m They chew the leaves of this indigenous narcotic in afternoon-long sessions to induce a pleasurable state of low-level mental stimulation.

In businesslike South Yemen, qatm sessions are limited by government decree to the weekends, but in North Yemen the drug has become a national hazard. Large tracts of productive land are turned over to qatm cultivation as prices soar in the marketplace. Nearly all male citizens indulge a few days each week.

Qatm and the continued influence of tribalism have severely blunted the impetus to plow money earned abroad into building up the country. Political instability continues, with the government swinging wildly between ideological extremes.

Could such instability spill over into Saudi Arabia and the rest of the peninsula? It was significant that some of the Saudi religious fundamentalists involved in the Mecca Grand Mosque takeover of 1979 came from the Najran and Asir provinces.

One Attempt to stem the tide of Yemeni-inspired destabilizing influences has been made by nearby Oman. Between 1969 and 1975, South Yemen backed leftist insurgents in oman's western provinces: Oman's firmly pro-Western Sultan eventually repelled them with the help of Iranian troops lent by the Shah. But bringing in Iranian troops made him something of a pariah in the peninsula. He was unable to follow up his success on the battlefields with any political moves to tie South Yemen closer into mainstream peninsular developments.

That is a role the sophisticated diplomats of Kuwait are now exploring. They have tried to mediate in the most recent wrangles between the two Yemens, and between each of the Yemens and Saudi Arabia. They have sweetened their overtures, meanwhile, with generous offers of development aid to both Yemens and tried to persuade the Saudis to match them.

Such efforts, coming from Kuwait, show the extent to which development and stability are increasingly being seen by the government and stability are increasingly being seen by the governments of the peninsula as a shared concern.

It remains to be seen whether the Soviets, from their foot hold in Aden, share this view. But already, as turmoil haunts to one side the Iraq-Iran region, to the other the Horn of Africa, the ancient people of the Arabian Peninsula seem once again to be looking to one another for support.