A truck containing grenades, uniforms and guns has been found after Wednesday's attempt to kill President Lansana Conte, police say.
President Conte won a third term in 2003 elections despite poor health
The truck was found near the site of the assassination attempt, they say.
Some of those arrested have been released but others are still being questioned by the security forces.
The BBC's Alhassan Sillah in Conakry says he understands that those arrested are not well known personalities or politicians but local residents.
He says that even some opposition politicians have stepped up their security after the attack.
Heavy security surrounds presidential and national media buildings. Checkpoints have been set up in many areas of the capital as police search for the gunmen.
On Thursday, Mr Conte appeared in public, going to the mosque for prayers on the Muslim holiday of Eid-el-Kebir.
He has said those who tried to kill him are wasting their time and only God would decide when he went.
Unidentified men fired on the presidential convoy taking Mr Conte to work. The president escaped unscathed.
Our reporter says a dispatch rider who was leading the presidential motorcade was seriously wounded in the shootout and is now in intensive care.
After opening fire the gunmen threw away their weapons and disappeared into the crowd, eyewitnesses say.
Most residents are confused that such a daring attempt could be made on the president's life in broad daylight, our correspondent says.
The president - who seized power in a coup in 1984 - has hinted that an unnamed foreign power may be behind the attempt.
The incident happened a year after President Conte was sworn in for a third term, following his victory in controversial elections in December 2003, after the constitution was changed to allow his to stand.
Celebrations to mark the occasion were dampened by the shooting, our correspondent says.
Mr Conte is a diabetic, and correspondents say doubts about the president's health have led to worries about a possible future power struggle.
Guinea, a mineral-rich country bordering Sierra Leone and Liberia, has been viewed as generally stable in an otherwise turbulent region.