Leaders of the 10-member Association of Southeast Asian Nations (ASEAN) announced the adoption of the joint declaration at their summit in Cambodia.
The Philippines Foreign Secretary Albert del Rosario has described the agreement as a "legacy for the region's children".
But rights advocates say it falls short of world standards, and allows too many loopholes for governments.
"Our worst fears in this process have now come to pass," said Human Rights Watch deputy Asia director Phil Robertson.
Leaders at the summit in Phnom Penh are expected to discuss the ethnic violence in Burma, where clashes in Rakhine state between Muslim Rohingyas and Buddhists have left 180 people dead since June.
ASEAN secretary-general Surin Pitsuwan told AFP news agency the violence was disturbing and risked destabilising the region.
He says leaders would discuss the bloodshed and potentially include a statement referring to it in their end-of-summit communique.
Another point of contention during the three days of top-level diplomacy in Phnom Penh was likely to be the territorial rows over the South China Sea.
China insists it has sovereign rights to nearly all of the sea, including waters near the coasts of its Asian neighbours.
Vietnam, the Philippines, Malaysia and Brunei, as well as Taiwan, also have sometimes overlapping claims to the sea.
The rival claims have for decades made the waterways, home to some of the world's most important shipping lanes and believed to sit atop vast natural resources, a potential military flashpoint.
Tensions escalated this year amid complaints by the Philippines and Vietnam that China was becoming increasingly aggressive in staking its claim to the sea.
The ASEAN chief says the regional bloc will present a united front to Chinese Premier Wen Jiabao at the East Asia Summit.
On Saturday Mr Surin floated an ASEAN proposal for a hotline with China aimed at easing maritime tensions.
The ASEAN summit will be expanded into a two-day East Asia Summit starting Monday that includes the leaders of the United States, Australia, China, Japan, India, South Korea, New Zealand and Russia.