Israeli diplomats are meeting with their counterparts and decision-makers abroad as part of the new effort, Foreign Ministry spokesman Yigal Palmor said.
"People abroad perhaps do not understand the real distress of Israelis in the south who live with the rocket threat. Then you wake up in the morning with an Israeli response and you don't understand where it came from," Palmor said.
Israel's U.N. envoy was sending a letter to Secretary-General Ban Ki-moon stressing Israel's concerns, he said.
Ministry officials said the diplomatic moves were in part a pre-emptive step to block any U.N. Security Council resolution that could interfere with an Israeli operation. They spoke on condition of anonymity because the specifics of the Israeli moves were not officially made public.
Prime Minister Ehud Olmert and Defense Minister Ehud Barak met last week and decided to green-light a Gaza operation, but left the timing vague.
Israeli leaders have made similar decisions repeatedly in the past. Some experts say Israel's government isn't really interested in a military offensive, and the flurry of recent activity is only the government scrambling to show the public that it is taking some form of action.
Hamas has transformed itself from a ragtag militia to a highly organized and well-armed force, and Israel's military is wary about potentially high losses in its ranks in an operation that would have uncertain results.
"There is real concern in the military and the defense ministry about the price, and they are trying everything not to go into Gaza," said Reuven Pedatzur, a military analyst at Tel Aviv University.
But if rockets kill a large number of Israelis, he said, "they won't have a choice."
In the past, Israel's military incursions into Gaza have ended with high Palestinian casualties and no long-term reduction in rocket fire.
Israel pulled all of its troops and settlers out of Gaza in 2005, a withdrawal that was followed by more rocket fire by militants and a violent takeover by the Islamic group Hamas.
A six-month truce between Israel and Hamas officially expired Friday after unraveling over a period of weeks. Israel has largely sealed Gaza's border crossings since early November in response, causing shortages of fuel and basic supplies. On Monday, Gazans lined up at bakeries as flour supplies threatened to run out, and the territory continued to be plagued by power shortages.
The militants' rocket range now includes a significant swath of Israel's south, including the oft-targeted town of Sderot and the city of Ashkelon, a major center of 120,000 people.
Yuval Diskin, who heads the Shin Bet security service, told Israel's Cabinet on Sunday that militants now have rockets that can reach as far as the important port of Ashdod and the south's biggest city, Beersheba, 25 miles from Gaza, according to an official present at the meeting. He spoke on condition of anonymity because he was not authorized to officially release the meeting's contents.
