The blackout that struck New York this week might have been avoided if Consolidated Edison Co. had been generating more of its own electricity instead of buying it from outside suppliers.

That is what Con Ed officials told members of the Federal Power Commission in New York yesterday on the first day of what promises to be a two week investigation of the blackout that darkened the city of 9 million for up to 25 hours on Wednesday and Thursday.

Con Ed was importing from Long Island, New Jersey and upstate New York as much as one third of the 6 million kilowatts it was passing on to customers Wednesday night. Two lightning strikes knocked out Con Ed's two biggest generators that night, creating such a shortage of power inside Con Ed's own jurisdiction that it posed a threat to the outsiders exporting power to Con Ed.

The power exporters shut Con Ed off as soon as they realized Con Ed was shutting down its Indian Point nuclear-powered plant and its Ravenswood oil-burning plant. The exporters feared that Con Ed's rising demand for their electricity would trigger blackouts in their own districts.

As soon as upstate New York, New Jersey and Long Island withdrew their 2 million kilowatts, the Con Ed system blacked out. Con Ed was generating only 4 million kilowatts of its own for customers demanding 6 million.

Con Ed bought outside electricity because it was cheaper that what it could generate at its own plants, many of which were idle the night of the blackout. Con Ed has followed a policy for the last two years of buying power from other suppliers if it is cheaper than its own.

"The city and the state Public Service Commission watch Con Ed like hawks on its fuel-buying policy," one source said. "Con Ed is always comparison shopping for cheap power."

The power Con Ed was buying came from utilities with nuclear, hydroelectric and coal-burning plants, all of which are cheaper to run than Con Ed's oil burners. Even Con Ed's oil-burning plants are required to use fuel containing no more than 1 per cent sulfur, the most expensive oil on the market.

Hand Con Ed been operating its own idle generators Wednesday night, it might have been able to black out Westchester County selectively and keep New York City running.

"I can't say for sure we could have avoided a complete blackout," a Con Ed source said, "but a blackout would have been much less likely if we had our own generators supplying that 2 million kilowatt difference."

Adding to the fragile nature of the Con Ed system is the lack of automatic devices anywhere in Manhattan for Con Ed to black out portions of the city selectively in order to keep other sections going.

City regulations stipulate that these devices be placed underground, and Con Ed has never installed them below ground in Manhattan because the excavation work alone would costmore than $100 million.