An economic crisis is forcing changes in Yugoslavia, where communism first embraced consumerism but got carried away on a float of costly western credits.

This one-time model socialist system's single-party rule is not in question, and the Communist bosses who have governed here collectively since president Josip Broz Tito's death in 1980 say there will be no rewriting of fundamental national principles on worker self-management or East-West nonalignment.

But within these bounds, a number of influential voices are contending that Yugoslavia's political and economic systems will have to be altered if the economy is to recover and schisms between the country's eight strong-willed constituent republics and provinces are to be avoided.

Recognizing Yugoslavia's strategic significance as a bulwark against the Soviet-led Warsaw Pact reaching the Mediterranean, western governments and banks are fashioning a $4.5 billion financial rescue package to help prop up this Balkan nation.

The Belgrade government has instituted a series of emergency austerity measures to boost exports (a 20 percent devaluation of the dinar), to save energy (gasoline rationing) and to preserve foreign exchange (a tax on foreign travel). Recently, some communities introduced ration cards to cope with shortages in cooking oil, detergent and coffee--a jolting step for a people who in the past decade had become Eastern Europe's freest spenders.

It was this spending, poorly controlled and drawing heavily on foreign credits, that got Yugoslavia into its fix. Servicing a $19 billion debt has put an enormous strain on an economy crippled by a 30 percent inflation rate, foundering exports, a forced cutback in imports and no production growth.

"Our ambitions were greater than our funds," explained Borisav Srebric, a vice president of the Federal Executive Council. "We ended up borrowing to make up the difference. Now our economy has entered a very difficult phase of adaptation."

Yugoslav officials figure their recent stopgap measures have bought time for member republics to negotiate longer-term economic and political reforms over tightly held regional interests.

To this end, a long-awaited report by a special commission considering economic changes is expected this spring. Parallel to the economic study, authorities have taken up calls for political corrections.

A much publicized letter last autumn to the Federal Presidium of the League of Communists from Najdan Pasic, president of Serbia's Constitutional Court, urged "more rationality and effectiveness" in the political system.

Pasic warned that "in major areas of social life, things have been moving in a diametrically opposite direction from what had been foreseen in various programs, plans and decisions." He also said the self-management system had been stagnating and that large areas of economic, political and ideological life had been "seized by processes of disintegration."

Similarly, Kiro Hadzivasilev, a party Presidium member from Macedonia, spoke recently of the need for "ideological innovations" to carry Yugoslavia's revolution further.

None of these outspoken invitations for change has been specific in prescribing new forms. But they point to growing party support for initiatives that would revive the country and steal the thunder from the nation's two main dissenting wings--those who advocate more centralization of authority and those favoring a multiparty system.

Part of Yugoslavia's economic problems is keyed to the world recession. But inefficiencies in the highly decentralized system here, in which individual republics and groups of workers have a major say in running their affairs, are widely viewed as responsible for turning the international slowdown into a national crisis. Republics and provinces often have interpreted their autonomy as economic self-sufficiency. Each has sought its own infrastructure. Ill-coordinated investment has led to duplicated steel mills, oil refineries and other major projects.

Central control on foreign borrowing has been weak. Goods, capital and foreign exchange do not flow freely in an internal market increasingly fragmented along regional lines.

Along with this atomization has come a concentration of power in state and local agencies. This has complicated national decision making.

A provision in the 1974 constitution listing only certain issues as requiring a consensus among the republics is virtually ignored in practice. Even the most minor concerns are subjected to time-consuming negotiations between regional representatives. Political paralysis often results.

Cutting through the stalemates, the government of Prime Minister Milka Planinc has imposed stringent limits on spending and investment. A 20 percent cut in capital investment is projected for 1983, together with a 7.5 percent decline in real wages and salaries. Belgrade authorities have made clear that temporary measures will be forced through until the republics can agree on other plans.

The Yugoslav national bank, under pressure from western lending institutions, has adopted new supervisory controls over regional bank practices and begun pooling foreign currency earnings to facilitate essential payments.

Such centralizing moves go against the grain of Yugoslavia's basic self-management tenet and are taken only hesitantly by officials.

Some strengthening of the central state apparatus may be unavoidable if Yugoslavia is to integrate economic groups and reduce the omnipotence of state and local agencies. At the same time, some decentralization will remain inevitable and necessary in a country of 18 nationalities.

The collective leadership principle evolved under Tito's tremendous personal authority, which held the system together as planets around a sun. His death has left Yugoslavia managed by committees of rotating chairmen who lack the stature of the old boss and his national focus.

"If Tito were alive, we'd certainly overcome our subjective differences more quickly and make some real changes," said Srebric, the Federal Council vice president.

The prospect of an actual rupture of the system is rated as unlikely, but so is the emergence of another strong leader.

Up to now, authorities have counted successfully on a wide margin of public patience. Despite general grumbling and unhappiness with curbs on consumption, relatively little labor unrest has been reported.

"The establishment is less likely to come into blame here than in other socialist countries, both because the investment decisions have been more decentralized and because everyone, not just officials, has been overspending," said Prof. Ljubisa Adamovich, chairman of Belgrade University's Department of International Economics.

"The problem here hasn't been a matter of a discrepancy between rich politicians and the masses. They had their Mercedes but I had my Fiat. It's been a difference between drivers rather than between those who drive and those who walk."

Nevertheless, a riot in Titograd last month in which dozens of stores were looted or had windows broken was provoked by a shortage of detergent and suggested that public tempers may be closer to exploding than officials concede.

Officials worry that dissatisfaction with the economy could prove a catalyst for political protest and a revival of divisive regional sentiments. Such concerns are evidently behind the recent party offensive against several leading newspapers that have reported aggressively on corruption, mismanagement and the general economic situation.

Meanwhile, hoping to ease public discomfort and tensions, the government has allocated part of its precious hard-currency reserves for imports of some scarce consumer goods, including raw materials for the processing of detergent.

"I wouldn't expect any disturbances like in Poland," a senior editor of a Belgrade paper said. "But Yugoslavs are very sensitive on political matters and the economic situation is causing a certain political nervousness. What politicians are trying to do by 'stabilizing' things, as they say, is to prevent any possible provocation."

Much of the problem today involves mustering a renewed political will to realize laws already on the books. Among the new thrusts, analysts predict, will be efforts to break down barriers to trade between regions, strengthen enterprise associations to offset the power of government agencies and assign closer responsibility for business decisions.

Critics of the system find some encouragement in all this. But they complain that the Communist leadership is still failing to tackle what they say is the crux of the problem--the party's resistance to liberalization and democratization.