MANILA, SEPT. 3 -- Communist guerrillas taking advantage of the military disarray left by last week's failed coup attempt ambushed a Philippine troop convoy 50 miles east of Manila yesterday and took the year's highest toll of government soldiers, killing 21 and wounding five.

Reports reaching Manila today said only two soldiers in the column escaped injury when more than 200 guerrillas of the communist New People's Army attacked in Quezon Province.

The guerrilla band reportedly blew up a bridge to cover its retreat.

Meanwhile, in Cagayan Valley on northern Luzon island, six soldiers and firefighters were killed when communist rebels overran a municipal police station, news reports said.

The military announced that guerrillas have killed at least 40 soldiers, policemen and civilians since the coup attempt. The other casualties were in scattered assaults in Pampanga, Isabela and Negros Oriental provinces.

The attacks followed a warning earlier this week that the communists planned to intensify their activity following Friday's coup attempt. The uprising has widened the divisions already existing in the armed forces.

That coup attempt, which began with an attack on the presidential palace and a takeover of key military camps and television stations, was launched by young officers who said they were disgruntled at what they considered the government's softness in fighting the insurgents.

The rebellion exposed deep rifts within the military, with hundreds of soldiers around the country expressing support for the uprising by wearing arm patches with the Philippine flag upside down. Cadets at the Philippine Military Academy also have voiced sympathy for the coup participants.

The New People's Army said in a statement dated Aug. 29 and released earlier this week, "Intensification of the revolutionary war and other people's struggles is the correct response to the worsening strife among the reactionaries. Let us take full advantage of contradictions within the reactionary ranks."

Some military analysts expressed surprise at the attacks, saying that in the past the New People's Army, the military wing of the Communist Party, has not been able to move so swiftly to take advantage of political crises in Manila.

The guerrilla army had already stepped up its campaign to topple the government with a series of daylight assassinations of top law enforcement officials in cities. The NPA is also believed to have penetrated key labor unions -- particularly the May 1 Movement -- and to have been behind the violent nationwide transport strike last week to protest increased fuel oil prices.

It was the first time in Corazon Aquino's 18-month-old presidency that large numbers of people had taken to the streets to demonstrate against her policies.

Political leaders here said they suspect that the avowedly anticommunist officers who staged Friday's coup may have been trying to take advantage of the unrest caused by the strike, and a general belief that the government was on the defensive.

"The coup attempt rolled on the strikes that were the result of the oil price increases," Teodoro Benigno, Aquino's press spokesman, said in an interview the day after the coup. "They presumably felt it was time to hit because of the turmoil caused by the oil and fuel price increases."

With the apparent increase in guerrilla ambushes in the countryside, the communists' threat to resume their urban violence and the disunity in the military as it hunts for the coup leaders and thousands of soldiers who joined them, the government's problems seem to be mounting.

{Aquino is under increasing pressure from supporters and family members to dismiss her two closest aides, Joker Arroyo, her executive secretary, and Teodoro Locsin Jr., her special counsel, the Los Angeles Times reported. House Speaker Ramon Mitra, who met with Aquino Thursday, told the Times in an interview that the two men must be replaced. Aquino has made it clear that she considers the two indispensable and will not fire them.}

Meanwhile, there was growing speculation that the leader of the failed coup, Col. Gregorio (Gringo) Honasan, could still be in Manila, possibly preparing to launch an urban terror campaign of his own as part of his effort to destabilize the Aquino government and force a change in the armed forces leadership.

Military analysts said that Honasan probably could hide easily in Manila, using safehouses and enjoying the support of at least some members of the fractious military who are supposed to be looking for him.

After escaping by helicopter as his coup appeared to be collapsing, Honasan has managed to keep Manila off balance amid rumors that he will stage a comeback. Analysts said Honasan is an expert in psychological warfare, and the suggestion of another attack has already served a purpose by keeping the government and the military immobilized.

Honasan is believed to be leading a force of about 2,000 men. Another 1,300 rebel troops surrendered, but only about half of their weapons were recovered.