Shevaldin said the unit's capacity would be reduced in stages throughout the day, to 750 Megawatts at about 4 pm, then to around 250-300 Megawatts, at which point the reactor will be switched off with the press of a button.
The Ignalina plant, which supplies about 70 percent of all energy consumed in the Baltic states, operates two Chernobyl-type RBMK reactors with 1300 Megawatt capacity each.
Lithuania had pledged to close down Ignalina's unit one reactor by January 1, as one of the conditions to joining the European Union in May this year, and has pledged to close the entire facility in 2009.
The EU has been worried about safety at the Ignalina plant, as it operates the same kind of reactors as in Ukraine's Chernobyl nuclear plant, which exploded in 1986 in the world's worst civil nuclear disaster.
The EU has promised to finance the plant's closure, estimated at 2-3 billion euros (2.5-3.75 billion dollars) over 30 years, and has allocated more than 200 million euros to prepare decommissioning of the first unit.
The first unit started to operate on December 31, 1983, the second was launched in August 1987.