The cell is devised to run crisis management operations when NATO is not involved - an issue that has caused controversy with the US.
According to a document circulated by the Italian EU presidency, the EU and NATO would each put liaison teams at each other's military headquarters. The document is to be approved at the EU summit in Brussels beginning on Friday.
The EU would also boost its own military staff's ability to conduct early warning, situation assessment and strategic planning by creating a cell that could, under tightly limited circumstances, plan and run military operations.
NATO Secretary-General George Robertson welcomed the agreement and made clear the United States would not object.
"If (the proposals) are agreed and implemented in the spirit of complementarity between the two organisations underlined by all EU members in recent days, this will be a good deal for the EU and for NATO," he said in a statement.
Asked if the United States would be satisfied with a military planning arrangement, Robertson said: "I speak for the alliance, so I've got to be pretty confident that what I say usually conforms to what the consensus would be".
Many in Washington were suspicious of the EU's ambitions for its autonomous rapid reaction force, seeing it as a French-inspired drive to subvert NATO and curb US influence.
"Give the plant some water and it will grow and eventually become too big for that little pot"
Unnamed EU diplomat
The United States was particularly angered by plans - championed by France and Germany - to establish a separate military headquarters, branding them "the most serious threat" to NATO's future.
Paris and Berlin have since substantially watered down the plan in negotiations with Britain, Washington's closest ally.
Diplomats said Italy hoped Friday's summit session would endorse the agreement and task EU foreign policy chief Javier Solana to put it into practice.
A diplomat from one of the EU countries keenest to establish an independent military headquarters voiced satisfaction nevertheless that the heavily circumscribed planning cell would grow into something much bigger over time.
"Give the plant some water and it will grow and eventually become too big for that little pot," the diplomat said.
US Defence Secretary Donald Rumsfeld and Secretary of State Colin Powell sidestepped a public row over the issue recently, suggesting that Washington had accepted Britain's word that the plan was no threat to NATO.