OTTAWA — A secret study by Canada’s spy agency says insurgents wreaking havoc in Iraq would see a U.S. withdrawal of troops as ‘‘a significant victory’’ unless Baghdad first has a stable government.

The Canadian Security Intelligence Service paints a bleak picture of ‘‘dire proportions’’ in which determined fighters are exploiting divisions between the Shiite majority and Sunni minority.

‘‘Insurgents are constantly honing their tactics,’’ CSIS says. ‘‘They have demonstrated greater sophistication in targeting, operational planning and execution, as evidenced by increasingly lethal attacks.’’

The study was prompted by speculation last summer from Gen. George Casey, commander of U.S. ground operations in Iraq, about reducing personnel numbers.

While there has been no confirmation of such a move, rumours have persisted that the United States and Britain might scale back their troops.

A declassified version of the secret October study was obtained by The Canadian Press under the Access to Information Act.

CSIS notes the ‘‘spectrum of instability’’ in Iraq includes high levels of criminal activity, civil unrest, increased sectarian violence between Sunnis and Shiites, regular guerrilla action against allied forces, assaults on Iraqi authorities, sabotage, kidnapping and assassination.

The spy service notes some observers have argued that rather than prompt a descent into civil war, an American pullout may pacify anti-U.S. elements, impair the recruiting efforts of the insurgents and give the Iraqi state a new sense of purpose.

‘‘However, without having clearly established a stable democratic government, insurgents will likely perceive a U.S. withdrawal as a significant victory,’’ the study adds.

Critics of the U.S. military presence in Iraq took issue with CSIS’ assessment, saying the root cause of insecurity is the presence of foreign troops.

‘‘The report seems, more (than) anything else, to be an elaborate justification of extending the occupation of Iraq,’’ said Dylan Penner of the Toronto Coalition to Stop the War, who doubts forces will soon withdraw.

‘‘The greatest risk to lives over there right now is the occupation itself.’’