By Ari Rabinovitch

ASHDOD, Israel, Dec 30 (Reuters) - For many residents of southern Israel, the fighting in the nearby Gaza Strip is measured not in days or hours, but in the number of seconds they have to take cover when Hamas rockets rain down. In coastal Ashdod, where a woman was killed by a rocket on Monday, about 40 seconds elapse between the "Code Red" warning sounded over loudspeakers and the blast of impact.

The city is 35 km (22 miles) from north Gaza and, before Israel launched an air assault on Hamas on Saturday, had been untouched by the Palestinian Islamists' salvoes. Many of its 230,000 residents still cannot believe they are now under fire.

"We're still in shock. Never in my life had I heard a 'Code Red' in Ashdod," said Eli, a 40-year-old taxi driver.

The rockets, some homemade and others factory-produced and smuggled into Gaza, have killed four Israelis since the fighting began. Hamas has been deploying more powerful rockets by the day as part of a strategy it has dubbed the "Burning Oil Slick".

Israel has killed more than 380 Palestinians in the Gaza Strip barrage since Saturday and demands that any new truce in Gaza guarantee that the rocket fire end.

Eli, who gave only his first name, was one of the first to reach the slain woman. She had bolted from her car to seek shelter after a siren sounded, but tripped and fell in the street, where she was shredded by the shrapnel of a rocket.

"It was like a nightmare. And you can still feel the tension," he said.

Haim Rosen, 13, said he was constantly thinking about places where he could take cover if sirens sounded again.

"It looks like any other day, but it feels different," Rosen said during a break from riding his bicycle on sidewalks still crowded with pedestrians. "Until now, we thought the alarms would only be heard in Ashkelon or further south."

In Ashkelon, 20 km (12 miles) closer to Gaza, the "Code Red" gives people about 30 seconds to find shelter. Though residents are more familiar with the sirens, having experienced rocket salvoes in the past, their routine has changed.

Shopping malls are often closed and the municipality and other government offices work out of fortified rooms or in underground shelters.

But the impact is perhaps most felt in small Israeli border communities where residents can see Gaza from their backyards.

There, they have only a 10-second warning of incoming rockets. Should the Palestinians fire low-flying mortar bombs instead, these can be missed by Israel's radars entirely.

Many towns are empty, with women and children preferring to stay with friends and family who are out of Hamas's range.

Nitzan Shay, 42, a farm-hand who lives in Kibbutz Nirim, about 2 km (1 mile) from Gaza, stayed back to work the fields while his family moved north.

"It's mostly just the men who stayed here," he said. "And the older folks, who have seen wars before and are not scared of anything." (Editing by Alison Williams)

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