The government formed its investigative committee after blaming Monday's blackout on alleged mismanagement of the electricity distribution network. Its findings will be released in eight days, an official said.
"We will determine the causes and make immediate corrections," government spokesman Panos Livaditis said.
But at least one official said the problems that led to the outage could not be fixed in time for the Aug. 13-29 Olympics.
Greece's Public Power Corp. said it would now have its staff help monitor the electricity grid to ensure a blackout does not take place during the Olympics, a company spokeswoman said.
Chief prosecutor Dimitris Papagelopoulos ordered his investigation as government leaders and power company officials held emergency meetings into the power outage that left nearly two-thirds of Greece's 11 million people without electricity.
Papagelopoulos' order allows judicial investigators to begin questioning those who may be responsible.
A senior police official said steps had been taken to ensure a blackout would not affect security systems safeguarding Olympic venues and that sites had backup power supplies, such as generators.
"Our operations centers all have alternative energy sites. All the Olympic sites and command centers have backup power. A blackout will not be a problem for security at Olympic locations," police spokesman Col. Lefteris Ikonomou said.
The investigations came as the chief operator for Greece's electricity grid and the Public Power Corp., or PPC, exchanged barbs about who was to blame.
Evangelos Lekatsas, chairman of the Hellenic Transmission System Operators, which distributes the nation's electricity, warned that Athens risked another blackout during the Olympics if power consumption was high because of a heat wave.
Heavy use of air conditioners during Monday's 104-degree temperatures was partly blamed for the blackout.
The Public Power Corp. disagreed and said Greece had more than enough electricity to deal with such a problem. The blackout, it said, was caused by how the grid was managed.
Public Power spokeswoman Maria Beskou said the PPC had lost a measure of trust in the transmission company after the outage.
"We will have two to four people on alert after this. The trust we had is not there anymore," Beskou said.
Lekatsas' transmission company is state-controlled but operates independently of the PPC, which is about 55 percent-owned by the state. The remaining stake is traded on the Athens Stock Exchange.
Lekatsas argued the overall conditions that knocked out power to at least 7 million people can not be corrected before the games.
He added that a heat wave and heavy air conditioner use are key factors that could create another blackout.
A detailed study of the blackout and its causes is not yet available, but Lekatsas offered a general picture: a major system malfunction occurred as it tried to compensate for a crippled generating station near Athens.
The overburdened lines created a cascading shutdown over southern Greece and many islands.
Lekatsas said the concern is not based on a shortage of power, but how it moves through the network.
Most of the power generating facilities are in northern Greece, but half the country's population lives in the Athens area or nearby. Regulating the long-distance electricity flow during peak demand times, like the current heat wave, raises risks of future blackouts, Lekatsas said.
On Monday, a generator near Athens stopped working and forced other generators from northern Greece to bring more power to the capital. The grid, however, could not pump in juice quickly enough to cover the voltage drop, Lekatsas said.
"This caused the whole problem ... the problem is that most of our generation is in the north and the load is in Athens, the south. So, it is very important to have generating units also in Athens," Lekatsas said.
No major generating plants have been built in the Athens area for the Olympics.
Beskou disagreed that Athens needed more plants for the Olympics.
"It would be nice to have another 10 power units in Athens, but we have ensured we will have more than enough power during the Olympics," Beskou said.
Five new substations in Athens will ensure that power will be distributed properly, she added.
By Patrick Quinn