SINCE President Reagan is going to try to end the second ''cold war,'' it seems a useful exercise to check over what the Soviets have gained, or not gained, during this recent phase of history.
It began 10 years ago when the Portuguese pulled out of their two most important surviving colonies in Africa, Angola and Mozambique. The Soviets backed independence movements in both countries and became the main advisers, and suppliers, to the two governments that were set up in 1975. Soviet and Cuban troops moved in to provide military backbone. Both entered the world community as Marxist states associated with the Soviet Union.
This sent a shock wave through Washington. Secretary of State Henry Kissinger warned the Congress of dire consequences if the condition were permitted to continue. He wanted to have the CIA support opposition resistance groups, as was done recently in Nicaragua. Congress took a less pessimistic view and forbade American aid to the resistance movements.
At about the same time the Soviets were building naval and air bases in Somalia and in South Yemen, just across the entrance to the Gulf of Aden. This caused the possibility of a Soviet military grip on the eastern approaches to the Red Sea and Persian Gulf.
That was where and when the second ''cold war'' got started. Four years later , in December of 1979, it seemed in Western eyes to become far more serious when the Soviets took over the main cities of Afghanistan with a massive airlift. Were they reaching for control of the Indian Ocean?
Today the Soviets are still heavily in Afghanistan, but have not yet succeeded in pacifying it. Rebels, with some covert CIA help, have kept up a harassing operation that denies the Soviets a completed conquest. It has been a drain on their military and economic resources. It has been resented in both China and India. It stimulated a revival of NATO and helped persuade America's NATO allies to accept the new intermediate nuclear weapons in Europe.
As an exercise in empire building and influence projection, Moscow's Afghan venture probably goes down as a net loss.
Even before the invasion of Afghanistan the Soviet investment in Somalia came to an abrupt end. It was at its peak in 1975. In 1977 the Somalis turned the Soviets out in retaliation for Soviet aid to Ethiopia. In 1978 Soviet and Cuban troops, serving with the Ethiopians, defeated a Somali army. Moscow had gained air bases in Ethiopia, but lost its grip on the southern coast of the Gulf of Aden.
There are still 500 Soviet and 19,000 Cuban troops in Angola and 300 Soviet and 750 Cuban troops in Mozambique. But last March Mozambique signed a mutual nonintervention treaty with South Africa. In June the US lifted its ban on aid. Mozambique is edging its way back into easier relations with the West.
Angola still has Cuban troops, but 80 percent of its trade is with the West. Its revenue comes largely from oil that is pumped and marketed by the Gulf Oil Corporation. The Chase Manhattan Bank is a major source of new investment funds. A right-wing insurgency financed by South Africa and led by Jonas Savimbi has been raiding up to the very edge of the capital, Luanda. Washington is working for a deal between Angola and South Africa under which the Cuban and Soviet troops would leave.
In other words Moscow has little to show for those imperial investments in Afghanistan, Angola, Mozambique, and Somalia which were largely the cause of the ''second cold war.'' It can also look back on far more important earlier failures. China was its ally and client for only eight years, from 1950 to 1958. Egypt was part of the Soviet imperial system from 1956 to 1972.
Moscow retains a hard military grip on its smaller neighbors in Europe, but events during the ''second cold war'' have disclosed the essential fact that, with the exception of Bulgaria, all would get out if they could. As empire builders the Soviets could not hold a candle to the great British Empire builders - Drake and Hawkins, Raleigh, Wolfe, Hastings and the Clives.