MANILA, Philippines (AP) _ Suspected communist rebels on Monday attacked a mayor who is related to President Corazon Aquino, killing seven of his bodyguards and wounding him, police said.

It was the bloodiest attack in the capital area since guerrillas took up arms against the government 19 years ago.

Mayor Prospero Oreta of suburban Malabon suffered three gunshot wounds in the mouth, chest and arm, police said. He was reported to be out of danger after surgery.

Oreta, 45, is a brother-in-law of Rep. Tessie Oreta, sister of Mrs. Aquino's assassinated husband, former Sen. Benigno S. Aquino Jr.

Hours after the attack on Oreta, assassins shot dead the brother of a prominent leftist politician. The leader said he may have been the intended target.

Also Monday, communist rebels killed a bus driver and wounded his wife in suburban Pasay City, authorities said.

The killings occurred as military units around the country were on full alert in anticipation of stepped-up rebel attacks marking Tuesday's 19th anniversary of the 24,000-member New People's Army. The group is the military wing of the Communist Party of the Philippines.

Communist rebels have been blamed for killing more than 150 policemen and soldiers in the Manila area since last year. The rebels recently announced plans to intensify the killings, which in the past have been limited to one or two victims at a time.

Mrs. Aquino, in a statement, said she was dismayed by Monday's violence.

''I have always asked our people to resort to the ways of peace,'' she said. ''My hope is that as democracy in our country gains a strong foothold, violence and terror will gradually rescind.''

Oreta and his bodyguards were attacked as they traveled in two cars bound for a flag-raising ceremony at Malabon town hall two miles away. Police Cpl. Mario Odulio said Oreta's ambushers used AK-47 and M-16 automatic assault rifles as well as 9mm and .45-caliber pistols. They escaped in a van and a jeep.

Local news reports said that shortly after the ambush, a man called Manila police to claim responsibility on behalf of the Alex Boncayao Brigade, the leftist rebel unit operating in the capital. But Armed Forces spokesman Col. Oscar Florendo said police had not established the call's authenticity.

Florendo said the military was investigating whether the ambush on Oreta was in retaliation for the slaying of leftist youth leader Lean Alejandro in September. He lost to Mrs. Oreta in a hotly contested congressional race last year, and leftist groups had linked the Oreta family to his murder. The Oretas had denied any connection.

Seven hours after the Oreta ambush, three men in a car shot and killed the brother of Jose Castro, vice president of the Manila chapter of the leftist People's Party. He said he may have been the intended victim, and he added he had received death threats since Alejandro's death.