BELGRADE -- A serious deterioration in trade and tensions over accumulated debts have blunted efforts by Soviet leader Mikhail Gorbachev to improve relations between Moscow and the communist leadership of Yugoslavia, diplomats and government officials here say.

Last December, Gorbachev, whose reform policies echo some of the steps taken by the late Yugoslav president Marshal Tito after his break with the Soviet model three decades ago, toasted Yugoslavia's present communist leadership on its first official visit to Moscow this decade and has tentatively scheduled his own trip to Yugoslavia this fall.

The Soviet leader has stressed a policy of respecting "different roads" to socialism outside the Soviet Union and has invited Belgrade to expand its contacts with the Soviet Bloc. Yugoslav leaders and state news media have responded with praise for Gorbachev's efforts to reform the Soviet economy and political life.

However, a major slump in Soviet-Yugoslav trade, caused by falling oil prices and the inability of the two governments to agree on how to resolve the resulting $1.2 billion in Soviet debts to Yugoslavia, has clouded the relationship as well as the prospects for Gorbachev's visit, officials said.

Moreover, Yugoslav observers say sympathy for Gorbachev has not noticeably affected the Yugoslav national establishment's commitment to Yugoslavia's prevailing balance of economic and political obligations between East and West.

"There is no sentiment for changing the status quo because of Gorbachev," one western diplomat said. "On the contrary, the economic problem with the Soviets has dragged out so long that it is becoming political."

The Soviet Union has long been Yugoslavia's biggest trade partner, and an agreement signed last year called for exchanges worth at least $37 billion between 1986 and 1990. The Soviets supply Yugoslavia with oil and other raw materials, receiving in return machines and manufactured goods.

The trouble in this trading relationship developed when the world price of oil fell precipitously last year. Because exchanges between the two countries are based on prearranged volumes that cannot be adjusted quickly when prices change, Yugoslavia shipped goods worth about $1.2 billion to the Soviet Union for which it did not receive compensation.

The Soviets refused to make up the deficit with more oil deliveries, and the Yugoslavs refused offers of Soviet manufactured goods to fill the gap.

As a result, Yugoslav exports to the Soviet Union have plummeted as authorities on both sides have held up deliveries because of the payment problem. Exports fell 18 percent in the first six months of this year compared to the same period of 1986, official figures show. Overall Soviet-Yugoslav trade has declined by more than one-third since 1985.

Yugoslav officials indicated that a visit to the country in late June by Soviet Foreign Minister Eduard Shevardnadze had not produced a solution to the impasse, despite expressions of good will by both sides. A report on the visit published in the Yugoslav press said only that "efforts should be made to overcome the trade imbalance" so that economic cooperation "that would serve their long-term interests" could be developed between the two countries."

"This {trade slump} is not the intention; it is not a policy," said Oskar Kovac, a Yugoslav federal minister for the economy, in a recent interview. "It is just what is happening because of the failure to resolve the problem.

"There is no possibility for us to increase imports now from that region," Kovac said, referring to the Soviet-led Comecon trade bloc, "because there are no goods available that we want to import."

For Yugoslavia, the slump in Soviet trade is part of a general upheaval, caused by the oil price decline, in foreign economic relationships. Belgrade's once-strong trade with Arab nations has also declined, and its efforts to meet payments on a $19 billion foreign debt to the West have been complicated by troubles in collecting on the more than $3 billion it is owed by such countries as Iraq, Syria and Libya.

One consequence of the problems is that Yugoslavia's trade with the United States and other developed western countries is rising rapidly. Yugoslavia's sales to the United States increased 36 percent in the first six months of this year, and total trade is expected to reach a record $1.3 billion in 1987, officials said.

For Moscow, the drop-off in trade with Yugoslavia forms part of a general decline in Soviet economic cooperation with Eastern Europe since 1985. Moscow's trade with its six East European allies increased only marginally in 1986.