Just a day after electricity was restored to the last outage areas of Queens, City Hall and Con Edison on Thursday were bracing for another heat wave that could threaten the city’s power grid.

The weather forecast calls for the temperature to reach 89 degrees Friday and to soar into the 90s Saturday, Sunday, and Monday. Officials said the heat could exacerbate the damage sustained by feeder cables and transformers in Queens during last week’s hot spell, as well as put increased pressure on the rest of the city’s network.

A spokesman for Con Ed, Michael Clendenin, said the utility was encouraging residents in northwest Queens to “pay special attention” to energy conservation in the coming days because equipment is in a weakened state. He offered no promises about how the grid will hold up. “As with any heat wave, we’ll be monitoring the system very closely,” Mr. Clendenin said. He later added, “You can never ever guarantee that there won’t be outages, especially during a heat wave.”

The extended outages that plagued several neighborhoods in Queens occurred after Con Ed decided against shutting down the area’s network, which would have resulted in as many as 500,000 people losing power, but for a potentially much shorter period of time.

While Mayor Bloomberg has said the city was involved in the utility’s handling of the blackout from the beginning, he distanced himself yesterday from the decision not to shut down the network. “In the end, it was their decision,” he said at City Hall. “It was their network, and they have to answer for it.” He added that he did not know if it was the right decision. The state Public Service Commission has launched an investigation of the outage.

In anticipation of another heat wave, Mr. Bloomberg has said he is prepared to return major municipal facilities, such as the Rikers Island prison, to backup generators to reduce the burden on Con Ed’s network.

The mayor has long relied on his reputation as a technocrat who operates outside the realm of politics, but after facing harsh criticism for his handling of the Queens blackout, he has taken the offensive in recent days. When 16,000 customers in Staten Island lost power Wednesday afternoon, the mayor cancelled his evening schedule and rushed out to the borough to give a news briefing.

“I thought it’d be nice to show your face,” Mr. Bloomberg said. “Obviously, everybody is more sensitive after what happened the week before. But I’m not trying to do anything for show.”

He also acknowledged yesterday that he had postponed a planned trip to Ireland because of the impending heat wave, saying he thought “people would feel more comfortable if I were here.”

Mr. Bloomberg had been scheduled to travel to Dublin and Sligo, where he was to have unveiled a monument to the Fighting 69th, the famed city-based Irish brigade that has fought for America in several wars. In a statement issued by the mayor’s office yesterday afternoon, Mr. Bloomberg expressed regret for backing out of the trip, but said Irish officials had agreed to reschedule the events for next month. The mayor also noted that he did the “next best thing” last night: He ate dinner at Donovan’s, an Irish pub in Woodside, Queens.

The mayor’s decision does not appear to have sparked a transatlantic rift. “We understand fully the reasons why the mayor had to postpone his visit, and we look forward to seeing him in August,” a spokesman for the Irish consulate said. “He’s always welcome in Ireland.”