Giuliani: We've been 'caught with our pants down' with ISIS

ISIS attack on US soil inevitable?

The Obama administration confirm that some Americans who traveled overseas to fight alongside ISIS are already back in the United States

This is a rush transcript from "On the Record," September 22, 2014. This copy may not be in its final form and may be updated.

GRETA VAN SUSTEREN, FOX NEWS HOST: Well, it's what we all feared. For the first time, the Obama administration is confirming Americans who went overseas to fight alongside ISIS now coming back to the U.S.

Former New York City Mayor Rudy Giuliani joins us. Good evening, sir.

RUDY GIULIANI, FORMER MAYOR OF NEW YORK CITY: Good evening, Greta.

VAN SUSTEREN: Well, we all suspected it. Now the administration confirms it. Now what?

GIULIANI: Now we have to really redouble our efforts to try to find these people, to gather the intelligence. Unfortunately, this is a situation, ISIS, that we were caught really with our pants down, not knowing enough about them, not having enough information about them. It means that there's heightened security. I was just over at the United Nations. When I was the mayor, this used to be the worst week of my year, when we had, you know, 100 heads of state here and the amount of security that's necessary. I would say the amount of security in New York now is substantially higher than I have seen in a very long time. So this is something that -- this is something we have to take extremely seriously.

And then, of course, the call from ISIS to -- for people to go act on their own, that is very, very difficult to detect because you're not going to get -- you're not going to get communications that you can intercept. You're not going to have informants that are going to get you the information. You're just igniting all these people who are self-proclaimed jihadists to do whatever crazy thing they want to do.

VAN SUSTEREN: It's terrible. I don't need to tell you that 19 people did what they did in 2001. It was only 19. Now the administration is talking about 100. I think the administration is even understated. What they have done, they said it includes those who have gone, those who have tried to go, and some who have come back are in their 100. Then I look at it and say what about those who are still here who are recruiters? What about those who are still here raising funds? How many are really involved in the group?

GIULIANI: I seem to recall -- but I could be wrong, so I hesitate -- at one point, there was a number they put out, about 500, and now it's gone down to 100. So I think what that really indicates is the level of intelligence here is not very good, which, of course, is not very helpful. And the reality is this is a group that we don't have the kind of experience we had with al Qaeda.

And you know, there's a point to the withdrawal of the troops, too, that nobody makes. When we had 100,000 troops in Iraq and 20,000 or 30,000 troops in Afghanistan, we were getting a lot of information. When you have that many troops, running into people, they're interrogating people, they're gathering information, we get a great deal more information back. Since we now have no troops or maybe the 1600 that we just put in, you know, for a couple years now, we have been getting much less information than when we had a major military presence in the area of the world where people were planning to come here and kill us.

VAN SUSTEREN: You know, how in the world do, you know, when you think about all this, it's hard to think whether you're being an alarmist or being practical and it's just so hard to determine. But let me ask you about something else, National Preparedness Month. What's that?

GIULIANI: National Preparedness Month is named by FEMA to get people to prepare for the kinds of disasters that they have, disasters that can be big ones, little ones. Believe it or not, I mean, the disasters that happen most often are sinks and toilets and air conditioners and heating and blowing up or water pipes. What people should do -- I work with a company called Home Serve. What they're doing on September 25th is having National Tune-Up Day. What they're suggesting is you get all of these things checked out, and you go get yourself some protection against this.

Also, given this ISIS threat, people should start thinking about keeping in their homes flashlights, food, medical supplies, think about the fact that maybe, just maybe you might have to spend some time in your house, and not have everything available. Definitely have an emergency radio. I don't want to frighten people. No reason to get terribly frightened. But there's also no reason not to prepare. And if it isn't terrorism, it's a natural disaster, and the same preparation is need for both. But getting yourself some kind of protection for your water pipes and your heating and your air conditioning is really a good thing. Home Serve is a great company. There are other great companies. I happen to work with one of them, but there are a lot of good ones.

VAN SUSTEREN: I remember when I was a kid going around to the neighbors who had bomb shelters, you know, their dried food in case we got nuked by the Russians or something when I was a kid, so might want to check to see if the food is still there.

(LAUGHTER)

Anyway, Mayor, thank you, sir.

GIULIANI: Thank you very much, Greta.