KIEV, Ukraine (AP) _ The head of Ukraine's nuclear power industry argued on Tuesday that the decision to close down the Chernobyl plant should be reversed.

Mikhail Umanets, who was director of the Chernobyl plant when the world's worst commercial nuclear power accident occurred there in 1986, told a news conference that the expansion of atomic energy was vital for Ukraine's economy.

He said the power plant should continue to operate until the turn of the century.

Ukraine's parliament, which has led the opposition to nuclear power, imposed a moratorium on new reactors and has ordered the Chernobyl plant closed by the end of 1993.

Umanets is now president of the state-owned Ukrainian nuclear power monopoly, Ukratomenergoprom. His statements coincided with a World Health Organization conference in Kiev on humanitarian and medical relief for Chernobyl victims.

Ukrainian Health Minister Yuri Spizhenko told the conference that studies have shown that complications during pregnancy are between one-and-a-half and two times as frequent as before the Chernobyl disaster. He added that 60,000 Ukrainian children had unacceptably high levels of thyroid irradiation, and that more than 200,000 people had weakened immune systems.

Umanets pointed to the country's power shortage to bolster his argument. Power to industry is rationed during peak hours, all but halting the oil refining industry.

He said Ukraine is too dependent on imports of natural gas and should rely instead on its own uranium and coal. Nuclear power now accounts for 25 percent to 40 percent of Ukraine's electricity.

Ukrainian President Leonid M. Kravchuk last month ordered his ministers to find ways to increase public support for nuclear power, and to ensure the safe and uninterrupted operation of power plants.

The reactor that exploded at Chernobyl, spewing radiation, has been shut down permanently and encased in a steel and concrete ''sarcophagus,'' which reportedly is leaking. A second reactor at the plant stopped operating after a fire in October 1991.

Two of the plant's four reactors are still in working condition. One was re-started in October, after six months of repairs to correct faults that led to an accident last spring at an identical reactor near St. Petersburg. The other reactor is scheduled to resume operation within two weeks.

Umanets said the reactors should continue operating until their internal supplies of graphite are exhausted. That is expected in 2001 for one, and 1997 for the other.