SANTA CLARA, Calif. >> San Francisco 49ers linebacker Aldon Smith was charged Wednesday with three felony counts of illegal possession of an assault weapon, stemming from a party at his home in June 2012.

The Santa Clara County district attorney’s office said in announcing the charges that Smith is expected to surrender on his own later this month. The 24-year-old Smith is on an indefinite leave of absence from the NFC champion Niners while undergoing treatment for substance abuse at an in-patient facility following a DUI arrest Sept. 20.

"We’ve been aware of the incident, the serious nature of it. We’re all accountable for our actions, good and bad," 49ers coach Jim Harbaugh said Wednesday. "There’s a process, due process, that will take place. I don’t feel any need to comment further on it."

When asked whether Smith — who set a franchise record with 19 1/2 sacks last season — would play again this year, Harbaugh said only, "I don’t have any need to further comment on it."

On Monday, the coach said he had traded a few text messages with Smith, saying, "Heard that things are going very well, very positive reports back."

If convicted, Smith could face up to four years and four months in jail, the district attorney’s office said.

"The preamble to the assault weapons law states that each assault weapon ‘has such a high rate of fire and capacity for firepower that its function as a legitimate sports or recreational firearm is substantially outweighed by the danger that it can be used to kill and injure human beings,’" District Attorney Jeff Rosen said. "California’s prohibition of these powerful weapons is not about hunting or target practice. It is about interrupting the long history of death, carnage and grief assault weapons have inflicted on California communities."

Smith also is likely to face a suspension from the NFL, perhaps pushed back to next season or after his legal issues are resolved.

The 49ers issued a statement Wednesday.

"The 49ers organization is aware of the recent developments with Aldon arising from an incident at his home in 2012," the team said. "We recognize the serious nature of this situation, as does Aldon, and will continue to monitor it closely. As this is an ongoing legal matter, we will have no further comment."

Last month, Smith and former teammate Delanie Walker were named in a lawsuit filed in Santa Clara County Superior Court by a Northern California man who said he was shot at a party at Smith’s house on June 29, 2012.

The players charged a $10 admission and $5 per drink, the lawsuit said. Smith and now-Titans tight end Walker, 29, were allegedly intoxicated on Smith’s balcony when they fired gunshots in the air while trying to end the party, the lawsuit said.

Before the 2012 home opener last September, Smith was the passenger in a car during an accident in Santa Clara County in which the driver swerved to avoid hitting a deer. Smith sustained a cut beneath his right eyebrow. He apologized and insisted he had grown up.

Smith, selected seventh overall in the 2011 draft out of Missouri, had previously been arrested on suspicion of DUI in January 2012 in Miami shortly after the 49ers lost in the NFC championship game.

He is on the reserve non-football injury list while in rehab, and there is no NFL minimum for number of games he must miss while on the list.

Smith played in a 27-7 home loss to the Colts on Sept. 22 and had five tackles just two days after he was arrested and jailed on suspicion of DUI and marijuana possession. Smith apologized for his behavior after the game.

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AP Freelance Writer Michael Wagaman contributed to this report.