Marxist Ethiopia has just launched a major military offensive against secessionist forces in northern Eritrea Province, becoming the third Soviet-allied country in Africa to undertake such a campaign against its noncommunist opposition in the past three months.

The latest Ethiopian offensive fits into a pattern of similar efforts in Soviet-backed Angola and Mozambique to knock out insurgency movements there. The Soviet Union also is reported to be on the verge of starting a fourth major drive this year in Afghanistan to seal off the supply lines along the Pakistani border of the U.S.-backed, anticommunist forces there.

The almost simultaneous offensives against insurgencies in these four Soviet-backed Third World countries have all taken place since Mikhail Gorbachev came to power last March.

While views differ within the administration over the meaning of this, it appears to be part of the jockeying between Moscow and Washington over their respective "freedom fighters" in Third World conflicts as President Reagan prepares to meet the Soviet leader in Geneva on Nov. 19.

Earlier this month, Congress authorized an extra $300 million over the next two years to the rebels fighting in Afghanistan. They were already receiving $250 million annually in military and other aid from the United States.

Yesterday, in his speech at the United Nations, Reagan proposed negotiations sponsored jointly by the United States and the Soviet Union to resolve the conflicts under way in these countries and in Nicaragua and Cambodia that would involve both the warring parties themselves and the two superpowers in talks to achieve "an end to violence, the withdrawal of foreign troops and national reconciliation."

In almost all these conflicts, the warring parties have steadfastly refused so far to sit down at the negotiating table.

Ethiopia, Angola and Mozambique all have Marxist-Leninist governments and they are the Soviet Union's three closest allies in Africa. All three governments have recently been losing ground to local insurgencies and have called on Moscow and its allies for increased military aid to deal with the threat.

Some U.S. analysts believe Moscow is responding to these pressures primarily to show Washington it is capable of defending its hard-pressed Third World allies. The Soviet response has included supply of more sophisticated arms and a bigger role in planning and executing counteroffensives, directly and through Eastern Bloc countries.

The latest Ethiopian offensive began Oct. 10, a three-pronged attack to capture the headquarters of the Eritrean People's Liberation Front in Nakfa, in northern Eritrea. It is the eighth big Ethiopian military campaign in six years to try to crush rebel forces.

The rebel front's U.N. representative, Bereket Habte-Selassie, said five to six Ethiopian divisions, heavily armed by the Soviets with mechanized units and helicopters to land airborne troops, were involved in the latest offensive. Two divisions are reported to have been brought from the Ogaden region of southeastern Ethiopia to reinforce the more than 100,000 Ethiopian troops already in Eritrea and neighboring Tigray Province.

"They are trying to encircle Nakfa," Bereket said. He said the government offensive had been checked and the front's forces had begun a counteroffensive.

Interestingly, the same strategy of seeking to deliver a knockout blow to the insurgency by occupying its headquarters has been followed in both Mozambique and Angola by the Soviet-advised central governments in recent months.

The tactic worked in Mozambique, where on Aug. 28, government forces, aided by 3,000 Zimbabwean troops, destroyed the headquarters of the Mozambique National Resistance Movement.

The tactic failed, however, in Angola, where an offensive by the Soviet-armed Angolan Army to occupy the base of the National Union for the Total Independence of Angola (UNITA), led by Jonas Savimbi, got under way July 29.

After making substantial gains with the aid of Soviet-supplied tanks, jet fighters and helicopter gunships, the Angolan offensive was stopped in late September, 150 miles from Savimbi's headquarters.

Recently, Savimbi has repeatedly asked publicly for assistance from the United States to counter the central government's offensive. The administration has been debating whether to provide it.

There has also been a surge of fighting in Afghanistan recently. Soviet and Afghan forces are apparently about to launch a new offensive to seal off the rebels' supply lines before the winter snows begin, according to administration intelligence reports.

By contrast, it is the U.S.-armed counterrevolutionaries who since June have gone on the offensive against the Sandinista government, taking their struggle deeper inside Nicaragua and touching off some of the heaviest fighting there in years. The Sandinistas have been mobilizing for a counteroffensive with the aid of newly supplied Soviet helicopter gunships.