WASHINGTON — An unusual government search of Marine Corps defense attorneys’ offices at California’s Camp Pendleton could cast a cloud over dozens of criminal cases.

The search May 2, which lasted about two and a half hours, included investigators opening more than 100 case files compiled by defense attorneys, Marine Corps officers say. The search went beyond what was necessary and exceeded applicable legal standards, officers think.

“It’s unacceptable,” Lt. Col. Clay Plummer, the Marine Corps’ regional defense counsel for the West Coast, said in an interview. “We’re going to litigate this, to make sure this never happens again.”

The courtroom fallout might take time to settle, as defense attorneys with Camp Pendleton’s Legal Service Support Team Echo consider challenges for each of the cases in which investigators allegedly accessed files. Among other arguments, the defense attorneys could charge interference with privileged communications.

In theory, defense attorneys could go so far as to seek the dismissal of charges against individual defendants whose files allegedly were compromised. Lesser remedies could also be sought

In a statement Friday afternoon, Camp Pendleton officials said the commanding general of Marine Corps Installations West had appointed an independent, neutral judge advocate to review evidence seized during the search.

The judge advocate will “identify whether any potentially privileged material was improperly disclosed,” the statement said, adding that “due to the pending litigation, and the independent review of the search, further comment on the facts of this search would be inappropriate.”

“The search of (defense attorneys’) offices is a rare event,” the statement stressed.

Rule 502 of the Military Rules of Evidence specifies that a client “has a privilege to refuse to disclose and to prevent any other person from disclosing confidential communications made for the purpose of facilitating the rendition of professional legal services.” Marine Corps defense attorneys typically won’t even disclose whether a servicemember has talked to them.

The defense services office that was searched at what’s formally called Marine Corps Base Camp Pendleton is one of two at the sprawling Southern California facility. It’s the busiest defense office in the Marine Corps, typically staffed by about eight active-duty attorneys.

Nationwide, the Marine Corps Defense Services Organization typically represents more than 1,100 Marines annually at courts-martial and administrative hearings. The organization prides itself as “Marines defending Marines.”

According to several Marine Corps officers familiar with the May 2 search incident, it arose out of prosecutors’ interest in a defendant’s cellphone for a particular Camp Pendleton investigation. A defense attorney offered to provide the phone but wanted a judicial order first.

Instead, officers say, a prosecutor — known as a trial counsel — showed up accompanied by at least four armed Marine Corps Criminal Investigation Division agents. They had a search authorization, similar to a search warrant, but signed by a local commander rather than a judge.

The trial counsel escorted the agents into the defense offices, and then left. Wearing light blue latex gloves, investigators found the cellphone within about 20 minutes. Nonetheless, officers say, the search continued for another two-plus hours.

During the search, defense attorneys were reportedly blocked from leaving. A few surreptitious pictures were snapped. Attorneys also managed to contact Plummer, who oversees defense attorney operations at Marine Corps bases in California and Arizona.

“We believe these to be improper actions by the government,” Plummer said.

The Justice Department, for one, recognizes that searches of defense attorneys’ offices require a delicate touch. Chapter Nine of the U.S. Attorneys Manual specifies various protections, from drawing up search warrants for attorneys’ offices “as narrowly as possible” to creating a “privilege team” whose members can screen materials first.