President Obama Starts to Prep Speech Ahead of Arizona Memorial

President Obama has started forming the remarks he will give Wednesday night during a memorial service for the victims of the Arizona tragedy.

"The president began working on his speech last night, and he is thinking through what he wants to say. He will devote most of his remarks to memorializing the victims," a senior administration official tells Fox News' Mike Emanuel. Another official says the president will also thank the heroes that stepped up last Saturday.

The White House stresses this will not be a political speech, saying this is a memorial service and not a partisan opportunity.

The University of Arizona is finalizing the details ahead service that will honor the victims of Saturday's shooting that killed six and wounded several others, including Rep. Gabrielle Giffords, R-Ariz.

The event titled, "Together We Thrive: Tucson and America" will be held at the university's McKale Center and among those who plan on attending includes Republican Arizona Sens. John McCain and Jon Kyl. McCain will cut short an overseas fact-finding trip to attend the service.

University President Robert Shelton told reporters Tuesday the event will have no "political overtones."

Expected to speak at the event will be President Obama, university President Robert Shelton, state and federal officials and some students.

The event will also have a Native American blessing, a moment of silence and a poetry reading and presentation of a chain that the public signed.

All eyes will be on the president's remarks, which analysts say could be a defining moment in Obama's presidency.

"You have to summarize, you have to somehow embody the emotions of the nation. Not just say the right words. And that's a challenge for this president who can be eloquent but often not emotional," said former President Bush speechwriter Michael Gerson.

This will be the third time the president has addressed the tragedy publicly, first Saturday afternoon and then Monday from the Oval office after a meeting with French President Nicolas Sarkozy.

A White House aide says, "The president thought it was important to visit the Tucson community since this tragedy touched everyone there as well as throughout the entire country in some way. The president believes that right now, the main thing we should be doing is offering our thoughts and prayers to those who've been impacted and making sure that we're joining together and pulling together as a country."

Fox News' Mike Emanuel contributed to this report.