By Laird Harrison

SAN FRANCISCO (Reuters) - Proceedings opened on Friday in the spousal-abuse trial of San Francisco Sheriff Ross Mirkarimi as a presiding judge was assigned to the misdemeanor case, and he set jury selection to begin next week.

Judge Garrett Wong also said he would rule next Monday on defense motions seeking to bar key prosecution evidence against the city's top lawman, who has pleaded not guilty to domestic violence battery, child endangerment and dissuading a witness.

At a pretrial hearing earlier this week, Mirkarimi's lawyers asked a judge to exclude a 45-second video a neighbor shot of his estranged wife, Eliana Lopez, showing a bruise she said was the second such injury that her husband has inflicted on her.

The defense also has argued that statements Lopez made to neighbors the day after the alleged incident are inadmissible under the so-called hearsay rule.

Lopez, 36, a soap opera actress from Venezuela, has said she does not wish to press charges against Mirkarimi, 50, so her statements to her neighbors and the video footage of the bruise on her arm are considered critical to the prosecution's case.

After he was assigned the case on Friday morning, Wong said during a 10-minute afternoon session that he would hear arguments on various legal motions next Monday, then empanel a jury on Tuesday.

Mirkarimi, who earlier this month won a loosening of court-ordered restrictions on contact with his 2-year-old son, Theo, said during a break in proceedings on Friday that the boy was "doing fine," adding, "He's the apple of my eye."

Lopez was not present for the proceedings.

Mirkarimi was charged in the domestic battery case on January 13, five days after he was sworn in as the city's first new sheriff in three decades.

The incident in question stemmed from a New Year's Eve quarrel the couple had over her plans to take their son on a trip to Venezuela, according to a police affidavit and Mirkarimi's attorney.

Police said Lopez later showed two of her neighbors, Ivory Madison and Callie Williams, a bruise on her arm that she blamed on her husband, prompting Madison to shoot video footage of it.

Before Madison turned on the camera, she told police officers, Lopez told her, "'I'm not gonna talk; I don't want to be on this tape,'" the defense motion says. But Lopez did talk.

The video shows a mark on Lopez's arm while she says, "This happened yesterday, the end of 2011, and this is the second time this is happening. And I tell Ross I want to work on the marriage, we need help.

"I have been telling him we need help, and I am going to use this just in case he wants to take Theo away from me. Because he ... said that ... he's very powerful, and ... he can do it."

Defense lawyers Lidia Stiglich and Mike Hinckley insist that the only statements admissible as evidence if Lopez declines to testify are spontaneous remarks she might have made under duress. They describe Lopez's statements to neighbors as "the very antithesis of spontaneous declarations," saying they occurred the next day.

Mirkarimi, one of the founders of the California Green Party, served on the San Francisco Board of Supervisors before taking office as sheriff in January.

(Additional reporting by Ronnie Cohen; Writing by Steve Gorman; Editing by Tim Gaynor)