Even as this power-starved capital suffers through another winter of blackouts and industry shutdowns, five reactor towers are rising in a huge nuclear power complex under construction in the southeastern town of Cernavoda, monitored impatiently by top Romanian Communist officials.

The Cernavoda works have been mired for years in the delays, cost overruns and technical entanglements that so frequently accompany nuclear power. Yet the Romanians eagerly are pouring more money into the project and betting precious investments on the accelerated construction of two more huge nuclear complexes.

Here, as throughout Eastern Europe, planners speak of nuclear power with the kind of large-scale enthusiasm not heard in the West since the reality of accidents, waste disposal and utility bankruptcies sank in. "The most important thing for us is to have energy as soon as possible," said Tiberu Comanescu, the adjunct director of the Ministry of Electrical Energy. "We have taken special measures, and we have concentrated our forces. From now on we want to stress the nuclear program."

Romania's plans -- and its desperate needs -- are extreme for Eastern Europe. The drive for nuclear power, however, has emerged as one of the most important common factors shaping the development of Moscow's allies, which are only now feeling the jolt of cutbacks in Soviet oil supplies and steeply rising costs after being largely shielded from the oil price shocks suffered by the West in the 1970s. Coal, the region's chief alternative fuel, threatens severe environmental damage, and failings of management and hard currency reserves have crippled efforts at energy conservation.

The result is that the governments of Eastern Europe, and even Cuba, have been drawn into a massive investment in nuclear plants guided by the Soviets. All have launched ambitious construction programs, and each of their industries has been assigned components of the Soviet-designed stations for local production.

Eastern European leaders already claim substantial progress in the nuclear drive. The capacity of nuclear plants in the region doubled to 4,800 megawatts between 1978 and 1983 as Bulgaria, Czechoslovakia, East Germany and Hungary opened or expanded nuclear plants. Production is planned to increase by another 500 percent by 1990, when the various countries expect to produce between 20 and 40 percent of their electricity with nuclear generators.

Yet government officials and independent experts here and in three other Soviet Bloc capitals say nuclear energy is coming both too slowly and at too high a cost. While massive investments are distorting government budgets and even fundamental industrial production, construction troubles have pushed back plans for plant start-ups by years in every country.

Industry experts complain that the mandatory development by each country of a nuclear components industry with inflexible links to outdated Soviet technology is a sure recipe for more of the inefficiency and declining technological competitiveness Eastern Europe is struggling to overcome. Meanwhile, there has been almost no public discussion of safety and environmental problems, even though both Czechoslovakia and Bulgaria reportedly have had nuclear accidents.

Perhaps most significantly, the switch from Soviet-supplied oil to Soviet-designed nuclear plants has had the effect of guaranteeing Moscow's key control over its allies' energy supplies into the distant future, several experts said.

Although nuclear production is partially diversified, the Soviet Union remains the exclusive source for Eastern Europe of the enriched uranium needed to fuel the plants. Moreover, it has persuaded its allies to devote part of their nuclear investments to two large nuclear plants in the Soviet Ukraine rather than on their own territories.

Only Romania, the Soviet Bloc's habitual maverick, has attempted to build nuclear power plants without the Soviets, drawing on Canadian technology for the five nuclear units at Cernavoda as well as seven other planned generators. Yet Bucharest has been obliged to complement this already-ambitious program with separate agreements with Moscow for a 3,000-megawatt, Soviet-built complex in Romania as well as Romanian production of parts for Soviet-built plants in other countries.

At the same time, shortages of hard currency to buy parts and slow production by Romanian builders have led well-informed foreign experts to predict that Romania's first Canadian power unit will not be completed until 1990, 10 years after the first concrete was poured.

"The Romanian case proves that trying to build nuclear plants with the West doesn't work," said a Hungarian expert who asked not to be named. "We simply don't have the hard currency to pay for it. At the same time nuclear power is the only realistic energy alternative for us, so we have no choice but to deal with the Soviets."

It was Moscow that kept Eastern Europe largely out of nuclear power while the West was investing in it in the 1960s and '70s by offering abundant supplies of oil at subsidized prices. For example, when Polish officials tried to launch a large nuclear program in the 1970s, the Soviets effectively blocked it.

The Soviet attitude changed in 1979, when the Soviet Bloc's Council for Mutual Economic Assistance, also known as Comecon, adopted a long-range program for nuclear development that set goals for the construction of plants under Soviet supervision and divided production of components among the Eastern European states.

Hard-line Soviet ally Czechoslovakia soon emerged with perhaps the largest stake in the joint program. In addition to a domestic nuclear program that already has completed five of 12 planned 440-megawatt nuclear generating stations, Czechoslovakia invested heavily in a nuclear parts industry and now makes Soviet-designed reactors for export.

Construction has fallen behind schedule all over Eastern Europe. As early as 1982, a Comecon meeting complained of serious delays as well as safety and production problems, and an economic summit meeting in Moscow last year issued another call for faster work.

Meanwhile, officials around the Soviet Bloc continue to dismiss questions about safety and environmental protection as strictly western problems. Several said in interviews that nuclear waste disposal was a minor concern because all Eastern European countries ship their spent fuel rods back to the Soviet Union for reprocessing.