WASHINGTON — Cybersecurity is a potential “”nightmare”” for the Department of Homeland Security in the years ahead, as well as concerns about homegrown terrorists and intelligence sharing, officials said Tuesday at a seminar at Georgetown University marking the department’s eighth anniversary.

“”The nightmare that the DHS has,”” said Stewart Baker, a former head of policy at the department, “”is that a very sophisticated hacker, perhaps working for Hezbollah, manages to infiltrate our electric grid and to bring down power to a portion of the United States, not for an hour or two, but for days or weeks. This would create a major humanitarian crisis.””

Homeland Security Secretary Janet Napolitano said the rapid pace of change is the biggest issue with technology.

“”The problem with cyber is almost by the time you’re talking about something, they’re on to the next thing,”” Napolitano said. “”It is really a fast-moving field that, quite frankly, probably none of us are as good at understanding as somebody who’s 20 years old, so this is an area where we’re really trying to hire people.

“”And if there are students in the audience that have any cyber interest, I would ask them to see me after.””

Napolitano’s predecessor, Michael Chertoff, said he was most concerned about terrorists born in the U.S.

“”Most notable are homegrown terrorists,”” Chertoff said. “”What you see now is greater emphasis on recruiting Americans who are residents in the U.S. to become operatives, and that is challenging the model that we use for security.””

And Tom Ridge, the first Homeland Security secretary, focused on the problems of intelligence gathering. The department is a consumer, not a gatherer of information, which is a major challenge when facing such threats, he said.

“”The agency can only act based on the information it’s given,”” Ridge said. “”I still think, eight years later, one of the big challenges is making sure that the Department of Homeland Security has enough information.””

Napolitano said one of the department’s achievements that helps to lessen the threat of terrorist attacks is increased public participation in the security process, particularly civilians who report suspicious behavior or observations to authorities.

“”When you talk about Faisal Shahzad, what a great example of citizen involvement,”” Napolitano said, referring to the attempted car bombing in New York’s Times Square in 2010. “”A street vendor sees smoke coming from a vehicle he doesn’t recognize … he immediately notifies law enforcement and we go from that notice, in 53 hours, to the apprehension of Shahzad.””

Napolitano also cited improving international sharing of flight information as another departmental success. She said the U.S. and the European Union share information about passengers as soon as tickets are purchased, rather than after the plane has already taken off, as was the case when Ridge was secretary.

Baker agreed that improved cooperation has been a key success.

“”Until very recently, we didn’t know if somebody who was presenting himself to enter the United States was a convicted criminal or not in his home jurisdiction,”” Baker said. “”The integration of data systems so that it is risky for terrorists to try to get across our borders is, to my mind, the single success of DHS.””

Baker listed the separation of the FBI from Homeland Security, an overabundance of grants causing funding issues and the lack of sufficient technology at the Mexican border as major shortcomings of the department over the last eight years.

Ridge also mentioned technology as a failing in the context of airport checkpoints.

“”President (John F.) Kennedy in ‘62 said, ‘We’re going to the moon.’ We got to the moon in ‘69 — that’s seven years. It’s 10 years after (Sept. 11, 2001), and we still haven’t figured out the right piece of technology in our airports,”” Ridge said. “”So apparently it’s easier to go to the moon than come up with a piece of technology to be a little bit less invasive.””