Four U.S. Marines refused to answer rape charges against them Friday in the Philippines, prompting the judge to enter a not guilty plea for them in a case that has stirred emotions about the U.S. military presence in the former American colony.

The rape charges against the four are punishable by up to 40 years in jail.

The court hearing was the first public appearance by Lance Cpl. Daniel Smith, Lance Cpl. Keith Silkwood, Lance Cpl. Dominic Duplantis and Staff Sgt. Chad Carpentier since the alleged Nov. 1 rape of a 22-year-old Philippine woman.

Judge Benjamin Pozon of the Regional Trial Court of Makati — a Manila suburb — earlier threw out a Justice Department motion to reduce charges against Silkwood, Duplantis and Carpentier, and kept all of them as principal defendants.

Pozon said he could not allow a downgrade of charges against the three "on the basis of the evidence not yet presented."

CountryWatch: Philippines

Silkwood's lawyer, Jose Justiniano, said the defendants' entering of a plea may be considered a waiver of their right to appeal the decision not to downgrade any charges.

"We will file a petition ... with the Court of Appeals questioning that ruling," Justiniano said.

The Marines, wearing civilian clothes, entered the packed courtroom with several Americans believed to be U.S. Embassy staff. The four have been in the embassy's custody.

Journalists, barred from the courtroom, peered through glass panels to see inside, where the Marines sat on a bench on one side of the room, facing the judge. They were ordered to stand as a court photographer took pictures of them for identification. A court officer later read them the charges.

They were immediately whisked away afterward. Several protesters along a corridor outside the courtroom shouted, "Jail the rapists!"

Outside the courthouse, about two dozen members of the women's group Gabriela carried placards saying, "Jail the Yankees," and "Rage Against Rape."

The defendants belong to the 31st Marine Expeditionary Force stationed on the southern Japanese island of Okinawa. They had finished counterterrorism maneuvers with Filipino troops when the alleged rape occurred in a van at the former U.S. Subic Bay naval base near Olongapo city, west of Manila.

The U.S. Embassy has refused to turn them over to Philippine police, citing a provision under the Visiting Forces Agreement, or VFA, that lets U.S. authorities hold American servicemen facing a criminal case.

U.S. officials have refused to disclose their hometowns.

Former Vice President Teofisto Guingona, one of the prosecution lawyers who has opposed U.S. military presence in his country, asked the court to issue arrest warrants for the Marines and to detain them in a Philippine jail.

The court did not immediately grant his request. The judge cited an earlier Supreme Court ruling on the VFA's constitutionality, said private prosecutor Evalyn Ursua.

Ursua said private prosecutors have questioned the constitutionality of parts of the VFA — particularly one setting a one-year limit, starting from the arraignment, on a trial of U.S. suspects.

Another part in question is U.S. custody of the accused, she said.

The judge has not yet ruled on these issues, Ursua said.

"The pressure is on us to speed up the process," she said. "The clock starts today."