Near-record Soviet arms sales last year strongly underscored the Kremlin's conviction that using military aid and weapons sales is the most effective means to win friends and influence governments in the Third World, the CIA says in anew report.

The report said most of the sales were in Africa and the Middle East.

"The Soviet Union reinforced its Third World connections with military sales agreements of near-record size and economic pacts that seemed to ensure long-term Soviet involvement in several key less-developed countries," the intelligence agency said in a report made public last week.

The report said, however, that while the Soviet military aid program rose to almost $4 billion in 1977-the second highest since the $4.1 billion figure for 1974 - its economic assistance programs dropped to $392 million. That was the lowest figure in almost a decade.

"Moscow once again focused on military aid as its most effective means of building up influence in the Third World," the report said.

It mentioned radical Arab states as Syria, Iraq, Algeria and Libya, and the Horn of Africa, where its move into Ethiopia was seen as purely political.

But in addition to the political gains, the CIA estimates arms sales in the Third World meant about $1.5 billion for the Soviets in "hard currency" gains.

"These earings come at a partially opportune time following the large hard currency deficits of 1975-76 and reduced pressures on the Soviet Union to cut back imports of badly needed equipment, grain and semi-manufactures from the West," the CIA said.

The 38-page report said the Soviet Union's most decisive military supply action was in the Horn of Africa, but noted that despite the Kremlin's heightened interest in black Africa-"where its Cuban surrogates played an increasingly important role"-the bulk of its military commitment last year went to support radical Arab states.

In 1977, the Soviet Union agreed to sell some $3.99 billion worth of arms to Third World nations but actually delivered $3.3 billion in arms-a record figure as far as weapons deliveries are concerned, according to CIA.

"The record $3.3 billion in Soviet military deliveries in 1977 featured a large proportion of advanced weapons systems and naval craft. Egypt's ongoing peace initiatives toward Israel provided Moscow Further opportunities to cement relations with Algeria, Libya and Syria-members of the "Steadfastness Front' opposing accommodation with Israel."

In the economic aid column, the report said, "Communist aid commitments fell to their lowest point in nearly a decade in 1977-only $875 million in new credits. The most precipitious drop was in the Soviet program, as Moscow pledged less than $400 million, mostly to India."