Leaked reports show that the US general will argue that major changes in US strategy in Iraq can only hinder the scant security and political progress that has been made.
Crocker is also expected to discuss the challenges of corruption, reconciliation, and de-Baathification.
Petreaus will say the strategy of 30,000 addition troops is working better than any previous effort to stem internal fighting - securing the streets for ordinary Iraqis.
The US general in Iraq will also reject the withdrawal of troops, except in small numbers, and only in the spring. Just this week, in another leak, he was reported to have said, he would be willing to cut troops by at least one brigade if the situation on the ground allowed.
Meanwhile US politicians agree that a preview of the long anticipated Petreaus report can help sway public opinion.
"If you get it out in the media and repeat it over and over, you enforce the story upon people. And a lot of times it doesn't matter what the actual substance is," Larry Johnson, a former US state department official, told Al Jazeera.
Democrats trust Petreus will provide an honest assessment, but acknowledge he is in a difficult position.
Senator Jack Reed said: "In many respects I think Petraeus is playing the political role for the president. He is a splendid officer, a good soldier."
Earlier, President Bush said he was briefed by both Petraeus and Crocker who reported progress on the ground.
"I ask the members of congress to sit back and listen to what we all have to say before they reach the conclusions that they're going to reach."
Petreaus and Crocker will no doubt come under heavy questioning by US congressional leaders when they submit this report.
But given the number of leaks which have already surfaced, many agree that it is unlikely to contain any elements of surprise.