Peace Now director Yariv Oppenheimer said the government has taken significant steps to enforce the moratorium but that the newly documented violations show it has not been entirely successful.
"In some places the government doesn't know about it and in some places it is trying to ignore it," he told AFP.
An Israeli government spokesperson referred questions to the defence ministry, which could not immediately be reached for comment.
In an ordinary eight-month period 1,130 new homes would be built in the settlements, the group said, meaning that the government's "freeze" has only reduced construction by half.
And the 600 units are in addition to 2,000 housing units approved just before the freeze was imposed in November 2009. The full report is available online at: http://www.peacenow.org.il/site/en/peace.asp?pi=61&docid=4747.
Israel's hawkish Prime Minister Benjamin Netanyahu reluctantly agreed to the moratorium after months of US pressure aimed at reviving peace talks with the Palestinians last suspended during the December 2008 Gaza war.
The Palestinians rejected the move as insufficient because it excluded public buildings, housing projects already under way, and occupied and annexed east Jerusalem, which they view as the capital of their promised state.
Israel has adamantly rejected Palestinian demands that it extend the moratorium and expand it to mostly Arab east Jerusalem, which it annexed after the 1967 war in a move not recognised by the international community.
In June Peace Now said that because the settlers had prepared for the slowdown by approving a raft of new projects before it took effect, the partial freeze would have little impact if it were not extended past September.
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