A new classified intelligence assessment on Iraq says there has been significant progress in security since the last assessment was delivered in August, a senior military official said.

In most ways the new National Intelligence Estimate hews closely to the one delivered nine months ago. That document spoke of security gains since the increase in troop levels began in January 2007, the continued high rate of violence and uneven progress on the part of Iraqi security forces.

"It does not differ significantly from August's NIE," a congressional official said in describing the document.

The officials spoke on condition of anonymity because the report is classified. They noted that many of the conclusions of the report are already reflected in public statements and press reports.

Since the August report, Sunni tribes have solidified their resistance to Al-Qaeda-associated insurgents in Anbar and Diyala provinces, which has weakened the movement.

The National Intelligence Estimate is part of a series of periodic reports that offer the best consensus judgment of top analysts at all 16 U.S. spy agencies on major foreign policy, security and global economic issues.

Congress received the new report this week in advance of congressional hearings April 8-9 at which war commander Gen. David Petraeus and U.S. Ambassador to Iraq Ryan Crocker are scheduled to testify. Similarly, the August report was delivered shortly before Petraeus' highly anticipated September testimony.

The report does not take into account the recent battle in Basra, the unruly Shiite port city in the south, according to another congressional official.

The central government's recent attempt at cracking down on lawless militias there, especially those that profess loyalty to firebrand cleric Muqtada al-Sadr, could be a turning point for Prime Minister Nouri al-Maliki's government in Baghdad. Maliki, also a Shiite, abruptly dispatched his interior ministry and military forces to Basra last week to confront the militias and assert Baghdad's authority over the area.

In a departure from the January and August 2007 intelligence estimates, the intelligence agencies have declined to release an unclassified summary of its key points. National Intelligence Director Michael McConnell decided last fall that NIEs should not as a rule include an unclassified section because he believes analysts are less likely to be forthright in their writing if they believe the language will become public.

Late Thursday, Democratic Sens. Edward M. Kennedy of Massachusetts and Sen. Carl Levin of Michigan, the chairman of the Armed Services Committee, called for McConnell to release a summary, saying in a letter that the information "is critical to the public debate in the coming weeks and months."