MANILA, Philippines (AP) _ As President Ferdinand E. Marcos spoke to the nation today over government- owned television, the screen suddenly went blank. Rebel soldiers had seized the station, cutting off Marcos in mid-sentence.

Three hours later, Channel 4 was back on the air, with radio and television personalities backing opposition leader Corazon Aquino now before the cameras and microphones.

''This is the first free broadcast from Channel 4,'' said one announcer, who urged people to congregate around the station building to prevent a counterattack by Marcos' supporters.

At least four people, including two civilians, were injured after rebels led by former Defense Minister Juan Ponce Enrile and Lt. Gen. Fidel V. Ramos, the ex-deputy armed forces chief, seized Channel 4. A loyalist soldier and a rebel also were wounded in minor fighting.

The operation was led by Col. Mariano Santiago, a former land transportation commissioner who had left Marcos' government. Hundreds of onlookers cheered as the loyalists surrendered, and leaders of the rebels and loyalist troops hugged.

About 15 government soldiers were captured by the rebels but there was little sign of animosity. People crowding around the station gave food to the surrendered soldiers, and told them Filipinos should not fight one other.

At the time Channel 4 stopped broadcasting, Marcos was on the air from the presidential palace several miles away, denying reports that he had left the Philippines and that the rebels leaders, who broke with him Saturday, were in power.

Inside the station, announcers abandoned their booths and one employee, Isabel Cloma, was in tears. Witnesses said a rebel soldier used the muzzle of his gun to tear down pictures of Marcos and his wife, Imelda.

The pro-Aquino broadcasters, saying they had had no time to organize, appealed to Filipinos to film what was happening in the streets and bring their video cassettes to the station for broadcast.

''We want to give you correct information, objective information for your guidance,'' said the Rev. Ben Carreon, a Roman Catholic priest. He called on Filipinos to ''exercise sobriety'' and show self-discipline during the current turmoil.

A statement also was read from Mel Lopez, an opposition assemblyman whose family had owned the station until Marcos took it over when he declared martial law in 1972. Lopez said the station rightly belonged to his family, but that the reformists were free to use it.

Some of the rebel soldiers at Channel 4, describing themselves as ''reformists,'' wore yellow caps with words ''free the people.'' Yellow was Mrs. Aquino's color in her campaign for the Feb. 7 election, which she claims Marcos stole from her by ballot fraud and terrorism.

Santiago wore a yellow headband with the words, ''Ninoy forever.'' Ninoy was the nickname of Mrs. Aquino's husband, Benigno, assassinated in 1983 when he returned to Manila after self-imposed exile in the United States. Mrs. Aquino has called Marcos her ''No. 1 suspect'' in the slaying.

Although Channel 4 and radio stations inside the government broadcasting compound were under rebel control, several Manila radio and television stations, as well as newspapers, are owned by political allies of Marcos.