WASHINGTON (AP) _ The government filed charges Wednesday against a 37-year-old former graduate student who was shot on the White House lawn after scaling a fence with an unloaded gun. Officials said he had a history of mental problems and may have acted out of suicidal impulse.

Leland William Modjeski, recently fired as a pizza delivery man, faces assault and firearms charges after he was apprehended less than 50 yards from the executive mansion late Tuesday night.

Federal prosecutor Eric Dubelier said there was ``some indication of a mental history.'' He did not elaborate, but an investigator speaking on condition of anonymity said Modjeski's wife had been concerned about his mental stability.

Two other law enforcement officials said investigators suspect Modjeski wanted to draw police fire. Officials stressed that the investigation was in its early stages, and a motive had not been firmly established.

Modjeski was not charged with attempted assassination, but officials did not rule out future charges. ``We have to figure out why he did what he did,'' Dubelier said.

FBI spokeswoman Susan Lloyd said, ``At this time, there is nothing to indicate it was an attempted assassination.''

Modjeski had earned a master's degree in psychology three years ago and had been admitted to the psychology doctoral program at suburban George Mason University in Fairfax, Va., near his home in Falls Church. He quit the doctoral program in 1992.

The incident was the third high-profile breach of White House security in eight months. It occurred just a few days after President Clinton closed Pennsylvania Avenue to traffic out of concern over the executive mansion's vulnerability to a truck bomb.

Police said Modjeski, wearing business attire, climbed a 10-foot, wrought-iron fence at the southeast edge of the grounds, setting off security alarms.

Uniformed Secret Service police officer Scott Giambattista spotted the suspect and approached him near where a limousine had dropped off Clinton half an hour earlier.

According to a Secret Service affidavit, Modjeski was holding a gun. Officer David Levine ordered him to drop the weapon. ``When Modjeski did not comply with Officer Levine's command, Modjeski was shot one time,'' the affidavit said.

Two law enforcement officials said Modjeski responded with the order to drop his gun by uttering an expletive at Levine. Investigators believe Modjeski may have been daring the officer to fire, the officials said.

``He wanted to be a cop-shot,'' one of the officials said.

The .38-caliber bullet, fired by Levine, apparently wounded both Modjeski and Giambattista. Modjeski's gun was unloaded, Secret Service spokesman Dave Adams said.

Estimates varied, but officials agreed Modjeski was 30 yards to 50 yards from the executive mansion when he was shot. They said the shooting occurred on a grassy area between the first lady's garden and the circular drive behind the White House.

Modjeski and Giambattista were expected to recover, although Modjeski may suffer minor nerve damage. Both were expected to remain a few days in George Washington University Hospital.

The latest breach of the White House left officials defensive about a security net toughened to historic levels with the weekend closing of Pennsylvania Avenue.

Clinton shrugged off the incident. ``Just another day at the White House,'' spokesman Mike McCurry quoted him as saying.

The president went for a morning jog at a nearby military base and called the wounded agent.

Prosecutors charged Modjeski with felony counts of forcibly assaulting a federal officer and interstate transportation of a firearm with intent to commit a felony.

Each charge carries a potential penalty of up 10 years in prison.

Neighbors in Modjeski's quiet neighborhood said they knew little about the man who had lived in the area for several years. His wife, Rose Mary, was interviewed by investigators but not held.

Modjeski was fired in November by a suburban Virginia Pizza Hut after less than five months on the job.

Security measures have been ratcheted up at the White House in reaction to a string of violent attacks on it the past eight months.

Foot patrols by federal officers were increased after a gunman sprayed the White House with bullets in October. A drunken pilot crashed his plane on the South Lawn in September in what police concluded was a suicide.

Administration officials said the shooting will not lead to another round of security changes.

Ronald Noble, who oversees the Secret Service for the Treasury Department, said only drastic measures, such as agents standing elbow-to-elbow around the White House, could end the longstanding problem of fence jumpers. ``That is not acceptable,'' he said of such a security arrangement.

Secret Service agents responded to intercept the intruder well before the president was threatened, Noble said. ``The system worked.''

Administration officials said they had feared that publicity about the street closing would generate copycats.

Modjeski joined a long list of fence jumpers at the White House, and he was not the first intruder shot on the grounds.

A report released Saturday to justify closing Pennsylvania Avenue said 23 people scaled the fence between 1989 and November 1994. A taxi driver who carried a pipe over the fence was shot and killed in July 1976.

A U.S. magistrate delayed Modjeski's court appearance until next Tuesday and appointed two assistant federal public defenders to represent him. Dubelier said Modjeski would be taken into custody upon his release from the hospital.