For Mayor Willie Brown, the first signs that something was amiss came late Monday when he got a call from what he described as his airport security - - a full eight hours before yesterday's string of terrorist attacks -- advising him that Americans should be cautious about their air travel.

The mayor, who was booked to fly to New York yesterday morning from San Francisco International Airport, said the call "didn't come in any alarming fashion, which is why I'm hesitant to make an alarming statement."

In fact, at the time, he didn't pay it much mind.

"It was not an abnormal call. I'm always concerned if my flight is going to be on time, and they always alert me when I ought to be careful."

Exactly where the call came from is a bit of a mystery. The mayor would say only that it came from "my security people at the airport."

Mike McCarron, assistant deputy director at SFO, said the Federal Aviation Administration "routinely" issues security notices about possible threats. He said two or three such notices have been received in the past couple of months,

but none in recent days.

Whatever the case, Brown didn't think about it again until he was up, dressed and waiting for his ride to the airport for an 8 a.m. flight to New York, where he was to attend a state retirement board meeting. That was when he turned on the TV, and like millions of other Americans, saw the twin towers of the World Trade Center crumble and the Pentagon go up in smoke.

Before the mayor was even out the door, District Attorney Terence Hallinan - - the man Brown said just last week should be recalled -- was checking in and offering help.

What followed was a conversation made up of equal parts gravity and formality.

"You know, you're the first call I've gotten on this," Brown said to Hallinan, as they were signing off.

With that, the mayor hung up and headed for City Hall. Along the way, he made the call to close all city buildings for the day and city schools as well.

He also talked with representatives of the Bank of America building and the Transamerica Pyramid, who agreed that because the structures were such high- profile symbols they too should be closed for the day.

Once Brown arrived at City Hall, calls were made in quick order to Municipal Railway director Michael Burns: "I want a complete backup in case anything happens to the subway tunnels," Brown said.

The Coast Guard: "To make sure the bridges were being protected."

And to the health, police and fire departments to make sure they were staffed for the emergency.

The last call went to Tom Ammiano, the mayor's longtime political nemesis and president of the Board of Supervisors.

"We may have to declare a state of emergency, although it's not something I want to do at this point because it kicks in all sorts of things -- but we may have to be ready," the mayor said.

Ammiano apparently agreed, because an hour or so later -- when the two sat next to each other at a city department heads meeting at the command center -- the call was made for only a "limited" state of emergency. One that would allow the courts, city offices and schools to close, but still keep the city pretty much in working order.

"What I want," the mayor said, "is for things to be to run as normally as possible, but sagely."

And for the most part they did. As for what comes next?

"With any luck, we'll be back to normal by tomorrow -- but with a heightened sense of awareness," Brown said as he sipped coffee with reporters at Citizen Cake on Grove Street.

But as for long-term safety?

"We can only do what we can," the mayor said, adding, "Hell, if they can't protect the Pentagon from attack, what can they protect?"

BART BLOCKS: Don't go looking for a rest room on BART -- they're all locked.

According to BART information officer Ron Rodriguez, a memorandum went out yesterday ordering all station rest rooms to be locked until further notice. They've also put out the word to watch for suspicious packages.

THE OTHER BROWN: Over in Oakland, Mayor Jerry Brown was trying his best to keep things normal as well.

"We're carrying on," Brown said. "I think the most important thing is for people to stay calm and understand that the power of terrorism is psychological.

"The goal is to sow disunity and to undermine our faith in the leadership of the country."

A few blocks away, Democratic pollster Paul Maslin sat in his office high- rise and wondered about the long-term effect of the attacks.

"It's like one part Pearl Harbor, one part Northern Ireland and one part I don't know what," was how Maslin summed it up.

Maslin -- who does polling for Gov. Gray Davis, among others -- said the strangest call he got yesterday was from one of the biggest Democratic consultants in Washington, D.C., who had just bolted his apartment.

"This was a grown man in his 50s, and he was scared out of his wits because he'd heard that a second plane was headed for the Pentagon," Maslin said.

"We can't even begin to gauge the long-term effects of this yet, but I will say, I don't think we'll ever be the same."