A 21-year-old Baltimore County man, whose Facebook postings about jihad gave way to discussions with an FBI informant about how to kill American soldiers, was arrested Wednesday after authorities say he tried to blow up a Catonsville military recruiting center using a car bomb supplied by undercover agents.

Federal authorities said Antonio Martinez, a recent convert to Islam who called himself Muhammad Hussain, watched videos of Osama bin Laden and mused about "dying for the cause" by joining militant forces overseas.

Unable to afford to travel to Pakistan or Afghanistan, Martinez instead proposed hitting local military installations to send a message. Officials say those plans culminated when he parked an SUV equipped with a dummy bomb in a suburban parking lot not far from his home.

It was the second FBI sting in as many weeks against an alleged homegrown terrorist trying to detonate a powerful car bomb, and like a recently foiled plot in Oregon, federal agents were watching the whole time.

Authorities described Martinez as a "lone wolf" who never posed a threat to the public and had no ties to terrorist organizations. But the investigation showed he was "absolutely committed to carrying out an attack which would have cost lives," said Richard A. McFeely, special agent in charge of the FBI's Baltimore field office.

The White House said in a statement that President Barack Obama had been informed of the operation prior to the arrest. The investigation "underscores the necessity of remaining vigilant against terrorism here and abroad and why we have been focusing on addressing the challenge posed by domestic radicalization," said Nicholas Shapiro, a White House spokesman.

The public defender assigned to represent Martinez cautioned Wednesday that people should not make assumptions about Martinez's guilt.

Court records show the operation came together quickly. After Martinez posted a vague comment on his Facebook page in late September, a confidential source notified the FBI and began engaging Martinez in conversations in which he shared his anger at U.S. military personnel.

"Each and every Muslim in this country … knows that America is at war with Islam and they're not doing anything about it," he said, according to a recorded conversation. "No one is stepping up to do anything. We have to be the ones to pull that trigger."

Martinez's plans to attack a military installation eventually focused on the Armed Forces Career Center in the 5400 block of Baltimore National Pike. He told a confidential informant that he knew how to get weapons, and sketched out how they could storm the building from the roof and "shoot everybody in the place."

He praised Nidal Hassan, the Army major who killed 13 soldiers in Fort Hood, saying Hassan had saved the lives of untold Muslims who would have been killed by those soldiers.

Martinez, who last lived in Woodlawn, was focused on acquiring rifles, but records show that an undercover FBI agent floated the idea of using a powerful vehicle bomb. With the seed planted, Martinez would inquire the next day about how to go about assembling such a device.

Muslims reacted with outrage and anxiety to news of the arrest. Muhammad Jameel, general secretary of the Islamic Society of Baltimore, which is located in Catonsville, spent the afternoon fielding questions from reporters and in prayer at the center's mosque, one of the largest in Maryland.

"We categorically condemn any criminal act, anybody who tries to hurt anyone" said Jameel, who has spent 40 years trying to transcend stereotypes about his faith. "Muslims always feel they are being subject to someone else defining what Islam is. This doesn't help."

Dr. Rashid Chotani, former president of the Howard County Muslim Council, said the arrest "is going to reflect very poorly on all of us." He said he feared the arrest could be a setback to years of effort to build better ties with government officials and people of other faiths.

"My biggest fear is children, how do they react to it," said Chotani, referring to both to Muslim children and those of other religions.

Wednesday's arrest closely mirrors a series of other recent FBI cases around the country in which U.S. law enforcement officials have used informants and undercover agents to shoulder up to potential terrorists, record them with hidden wires and other technology, and then arrest them when they try to set off bombs that the FBI knows will not detonate.

The arrests have come in Portland, Ore., where a man thought he was setting off a car bomb during a crowded Christmas tree lighting ceremony, in Chicago, where a man placed a backpack with fake explosives at a sports bar near Wrigley Field, and in the Washington metro area, where a man was scouting Metro stations in Northern Virginia and hoping to bomb the lines that feed in and out of the Pentagon.

"Stings are part and parcel of the toolbox law enforcement must have and must employ particularly in this kind of a terrorist environment," Homeland Security Secretary Janet Napolitano said after Martinez's arrest. "There are rules that govern them and they are done very carefully and the FBI abides by those rules, law enforcement abides by those rules, but they are an important tool to have."