A Canadian crown (government-owned) corporation is offering owners of building complexes a dandy new heating system. It's called ``Slowpoke.'' The big problem is this: It is nuclear-powered.

Atomic Energy of Canada Ltd. (AECL) maintains that its 10,000-kilowatt atomic heat source is perfectly safe. The small reactor sits in a huge, steel-lined concrete pool of water. It heats the ordinary, unpressurized water to only 95 degrees C., a bit below boiling.

A 2,000-kw demonstration model was commissioned last July in Whiteshell, Manitoba, and has been working fine. Slowpoke can be treated much like the oil-, coal-, or gas-fired boilers it would replace, an AECL sales pamphlet asserts.

But AECL hasn't even tried selling it yet in the United States, where antinuclear groups are extremely active.

Last month, however, AECL held a press conference to announce a potential customer: Three Hungarian companies signed a ``memorandum of agreement for cooperation'' with AECL that could lead to sales of 10 or more of the energy systems in that communist nation, where about 570,000 homes are already warmed by district heating systems.

Speaking of the nuclear nature of Slowpoke, Laszlo Rejto, the Hungarian trade commissioner here, commented: ``Nobody is so nervous because of this.''

When nuclear power is mentioned, probably most people think of huge plants generating perhaps 500,000 to 750,000 kw and involving pressurized water, massive container buildings to prevent the escape of radiation in the event of an accident, and the production of steam to turn turbines.

With Slowpoke, bundles of uranium fuel form a package about half the volume of a kitchen stove. The fuel heats the surrounding water, which then rises up a duct naturally to pass through heat exchangers near the top of the pool. Here the heat is transferred to a second stream of hot water that is pumped into radiators in the homes, apartments, offices, or other buildings that are part of the heating system. A building big enough to contain the plant would measure about 9 by 10 by 13 yards.

One load of fuel should last two or three years before needing replacement, depending on the buildings' demand for heat. AECL officials claim Slowpoke can operate unattended.

Despite the widespread public aversion to anything nuclear, companies in Switzerland and West Germany are developing similar small heating plants. A Swedish company suggests a much larger heating system using a pressurized water reactor like that in nuclear power plants.

But AECL officials believe they are ahead of their competitors with Slowpoke.

``Nuclear heating is the wave of the future,'' maintains Gerry Lynch, general manager of the crown company's local energy systems group. Fossil fuels (coal, oil, natural gas) ``should be preserved'' for use in transportation and the manufacture of chemicals. And nuclear heating would not add to acid rain or the ``greenhouse effect,'' he says.

With sales of AECL's large CANDU nuclear reactors stalled in recent years, the company has been seeking new sources of business - Slowpoke is one of them. AECL has been talking with Canadian utilities about the possibilities, but nothing has yet jelled. In the Canadian Arctic, there is a movement to keep the area ``nuclear free,'' even though Slowpoke offers potential economic advantages over other fuels.

The heating plants are not inexpensive. A Slowpoke would cost $5 million to $7 million (Canadian; US$3.9 million to $5.4 million), but would be capable of heating perhaps 1,000 apartments. This ``capital intensivity'' means the plant is only suitable for relatively cold climates. The cost would run about 2 to 2.5 cents per kilowatt, competitive with electricity, oil, and natural gas for heating.

Dr. Lynch sees the most potential for selling Slowpokes outside Canada, in places like Scandinavia, Eastern Europe, China, South Korea, and the Northern United States.

The Hungarian situation is seen as a ``natural fit'' and may result in a joint venture that would produce Slowpokes for Hungary and possibly other East European nations.

The system could be retrofitted to existing district hot-water heating systems with little alteration. It would save on the import of oil, coal, or natural gas now used in heating.

Lynch figures that about 50 percent of the labor and materials could be produced abroad, saving scarce hard currency for these countries.

The goal is to get the first Slowpoke installed in the early 1990s. But the two sides must agree on payment, the division of labor, and other details.

Dr. Rejto even talks of Slowpokes being used later for heating greenhouses that grow vegetables for Hungarians.

Earlier in the month Canada and Hungary signed a nuclear non-proliferation pact permitting the Slowpoke deal to be considered.