They also vow to work for "even greater unity" while allowing "different paces and intensity" of cooperation -- a notion which could fuel tensions among member states.
"We are determined to make the EU stronger and more resilient, through even greater unity and solidarity amongst us," says the draft document by 27 member states and EU institutions, dated March 16.
The declaration is likely to be subject to negotiation by EU nations ahead of a summit on March 25 summit, marking the 60th anniversary of the bloc's founding Treaty of Rome.
The one-and-a-half page text, a copy of which was obtained by AFP today, vows: "Unity is both a necessity and our free choice.
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"Taken individually, we would be sidelined by global dynamics. Standing together is our best chance to influence them, and to defend our common interests and values."
But it continues: "We will act together whenever possible, at different paces and intensity where necessary, as we have done in the past within the treaty framework and leaving the door open to those who want to join later."
But it is resisted by newer central and eastern European EU members, led by Poland, who fear being left behind.
The draft document, written in English, the bloc's main working language even though Britain is about to leave, may well be subject to change before the Rome summit.
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