Israel's leaders are expected to approve a ceasefire at a meeting later on Saturday, after which PM Ehud Olmert will address the nation, sources said to BBC.
The sources said the ceasefire deal did not involve Hamas.
It is not clear how Hamas will respond; its officials say the group will ignore any truce unless its demands are met.
Ahead of the move violence continued in Gaza, with 50 Israeli air strikes overnight. Rocket fire from Hamas militants also continued.
About 1,200 Palestinians have been killed since the violence began on 27 December. Thirteen Israelis - three civilians and 10 soldiers - have been killed during the campaign.
The Israeli move comes amid intense diplomacy aimed at ending the conflict.
Israeli sources told the BBC's Middle East editor, Jeremy Bowen, that Mr Olmert would announce an end to offensive military operations from "H-Hour", the exact timing of which is not yet clear.
Mr Olmert was expected to link the move to Israel having achieved its goal of curtailing rocket fire from Hamas-linked militants, the sources said.
If rocket fire continued after "H-Hour", Israel would respond, the sources said. If there was a single incident, Israel would hit back "surgically". If there were more attacks Israel would go back on the offensive, they said.
The sources stressed that this was a unilateral action by Israel. How Hamas responds remains to be seen.
Hamas insists that any ceasefire must involve Israeli troops withdrawing from Gaza and an immediate lifting of the Israeli blockade.
The announcement came on the 22nd day of violence in Gaza.
United Nations officials said two children, aged five and seven, were killed when Israeli tank fire hit a UN school where hundreds had taken shelter in the northern town of Beit Lahiya.
John Ging, the Unrwa chief in Gaza, told the BBC that there was "nowhere safe in Gaza".
"I'm ashamed of this - there's international legal responsibility to protect civilians in conflict, and we're not doing it," Mr Ging said.
An Israeli foreign ministry spokesman, Yigal Palmor, told the BBC that Israel was waiting for more information on what happened.
The Israel military said Hamas fired seven rockets into Israel on Saturday; there were no casualties.