US advisors have made several trips to the Philippines
Some of the US soldiers will train local forces to combat the rebel Abu Sayyaf group, which the US has linked with Osama Bin Laden.
The Philippine constitution bars foreign troops from operating in the Philippines, except for training purposes.
The news came as police in the Philippines seized a tonne of explosives and arrested three men with suspected links to the al-Qaeda network.
An army spokesman said the equipment was found during raids in the southern city of General Santos, and that 17 assault rifles were also discovered.
Presidential spokesman Rigoberto Tiglao has admitted that even Vice President Teofisto Guingona has raised questions over the plans to deploy US troops.
A former senator, Francisco Tatad, has accused President Gloria Arroyo of turning the Philippines into an extension of Afghanistan.
Nationalist fears
US Defence Secretary Donald Rumsfeld on Wednesday said as many as 250 US troops were already in the Philippines, but he said they were there for "logistics purposes" only.
He said some of the troops would accompany local soldiers in pursuit of the Abu Sayyaf rebels and would fire back if attacked.
Philippine officials have insisted the deployment is within the law. The US is a close ally of the Philippines and holds annual joint exercises.
The US is also a former colonial power, and nationalist sentiment in the country is opposed to US involvement.
John McLean, the BBC's Manila correspondent, says many Filipinos suspect the US wants to open a second front in its war on terrorism.
US hostages
He says there is speculation that the joint exercises are a cover for a US operation to rescue an American couple kidnapped by the Abu Sayyaf.
Martin and Gracia Burnham, from Kansas, were seized from a luxury tourist resort last May. It is thought they are being held in jungle on Basilan island, along with a Filipino nurse.
Our correspondent says people's suspicions about the US have been reinforced because the training exercises will include live firing exercises on Basilan.
The Abu Sayyaf is made up of a few hundred fighters who say they are fighting for independence for the country's Muslim minority.
However, their main activity is kidnapping for profit.