The Ashland man who pleaded guilty to terrorism charges Friday for plotting to fly explosives into federal buildings, was described by law enforcement officials as the type of lone wolf who would single-handedly carry out a terrorist act against the United States, in what prosecutors called a growing ­national security threat.

Rezwan Ferdaus, a 26-year-old US citizen, had no ties to Al Qaeda, but he sought out the terrorist organization with plans to blow up federal buildings in Washington, D.C., prosecutors said.

“He was a real, active threat,” said Jack W. Pirozzolo, first assistant US attorney for Massachusetts. “One of the things that is becoming an increasing part of our mission is to identify and contain and then bring to justice those lone wolves who would do harm.”

Ferdaus, who holds a bachelor’s degree in physics from Northeastern University, pleaded guilty in US District Court in Boston to charges of attempting to damage and ­destroy a federal building by means of an explosive, and attempt­ing to provide material support to terrorists.

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Several family members were at the courthouse to show their support, and shouted out, “We love you.” He leaned over to kiss his crying mother at the end of Friday’s proceedings, but was pulled away by US marshals.

Ferdaus will serve 17 years in prison followed by 10 years of supervised release, through an agreement he reached with prosecutors. As part of the agreement, prosecutors dismissed other terrorism-related charges. He had faced decades in prison and is slated to be sentenced Nov. 1.

Wearing tan prison garb, short hair, and a goatee, ­Ferdaus appeared to show defiance at the beginning of his hearing. He refused to stand when US District Court Judge Richard Stearns entered the courtroom. He also hesitated to stand and answer when a courtroom clerk asked whether he agreed to plead guilty.

But Ferdaus grow more ­cooperative, even polite, as Stearns guided him through a legally required process to ­assure he understood his rights.

He said he had a history of mental illness, of minor depression and anxiety, that he was suffering at around the time the investigation into him began. But he said he understood Friday’s proceedings. And he agreed with what prosecutors had alleged, that he plotted to send explosive-laden, remote-controlled airplanes, each about the size of a child, into the Pentagon and the US Capitol, and that he would shoot any personnel who fled those buildings.

Ferdaus, according to prosecutors, had told undercover agents posing as Al Qaeda operatives that his plan “ought to terrorize. It ought to result in the downfall of this entire disgusting place. That is my goal.”

“I want to totally destroy and take out the enemy, and take out as many [nonbelievers] as possible,” Ferdaus said, according to Assistant US Attorney B. Stephanie Siegmann.

Ferdaus was the second man from the suburbs west of ­Boston to be convicted of terrorism charges in the last year. In April, 29-year-old Tarek ­Mehanna, an American citizen from Sudbury, was sentenced to 17½ years for plotting to support Al Qaeda.

But legal analysts said that Ferdaus’s case was different in that he was actively plotting out a terrorist attack. Also, he ­appeared to be the mastermind: Siegmann told Stearns that Ferdaus designed the plan to fly the model airplanes into the buildings; he even took pictures of his targets. Ferdaus ­also visited Washington, D.C., and identified East Potomac Park as the launching pad for the planes.

Siegmann said that a confidential informant alerted author­ities to what Ferdaus was saying, and that the informant in turn introduced Ferdaus to two agents who were posing as Al Qaeda operatives. Ferdaus elaborated on his plans with them.

He also gave them 12 rigged cellphones that could be used to detonate explosive devises. ­Ferdaus taught them how to use them, even made a training video. “We’re changing the world,” he had said.

Ferdaus asked the agents, believing they were Al Qaeda, to provide him with guns and C4 explosives. He had obtained the planes. When he put the materials in a storage facility in Framingham, in September 2011, he was arrested.

Richard DesLauriers, special agent in charge of the FBI in Boston, said outside the courthouse Friday that the FBI’s counter-terrorism task force ­interrupted what had been a significant threat, by “detecting and preventing Mr. Ferdaus’s plot, the goal of which was an unlawful and violent affront to our nation’s cherished ideal of peaceful dissent.”

“Mr. Ferdaus’s decision to plead guilty demonstrates he conceived of this plot, acted of his own free will, and was solely responsible for his illegal acts,” DesLauriers said. “He admitted that he chose his own unlawful path.”