Media owned by the Hariri family accused the four, who include a top aide to President Emile Lahoud, of plotting the February attack that plunged the nation into turmoil.
But former pro-Syrian lawmaker Nasser Qandil, who was also detained in the probe, was freed after appearing before the UN commission of inquiry in Beirut on Tuesday.
The former security chiefs detained in dawn sweeps on Tuesday and the head of Lahoud's presidential guard Mustafa Hamdan, who turned himself in after an arrest warrant was issued, remain in detention.
Hamdan, as well as former general security chief General Jamil Al Sayed, ex-internal security head General Ali Al Hajj and former army intelligence director General Raymond Azar were questioned by the UN investigators and then brought before a Lebanese investigating magistrate on Wednesday.
The arrests were the first major development in the probe into Hariri's killing in a Beirut bomb blast on February 14 that has been widely blamed on former powerbroker Syria and its political allies in Lebanon at the time.
Al Mostaqbal newspaper, owned by the Hariri family, charged that the four had "held meetings to prepare for the crime".
"They also inspected the site of the attack the day before ... and [afterward] tampered with evidence at the scene to put investigators on the wrong track."
The paper also accused Qandil of "sending a message to the Syrian authorities underlining the need to get rid of Rafiq Al Hariri".
Syria's government daily Ath Thawra expressed fears on Wednesday of "seeing pressure from certain quarters to politicize the commission report".
But it added that, "despite all the attempts to put the blame on Syria, we have no doubt that the commission will confirm its innocence".
The United States described the arrests as a "very dramatic development", noting the officials' long-standing ties to Syria, and reiterated its complaint over the lack of cooperation from Damascus.
But Ath Thawra insisted that, "as President Bashar Al Assad has said, Syria is ready to cooperate fully with the investigation commission and provide it with all the information it needs.
"This is proof that Syria is working for the truth to come out and to unmask the true criminals, whose objective is to break up Syrian-Lebanese relations of coordination and fraternity."
Tuesday's arrests came just days after German prosecutor Detlev Mehlis, who heads the UN commission created in April, submitted an interim report to the Security Council.
Mehlis, whose commission has rounded up about 240 people for questioning since April, is due to hold a press conference in Beirut on Thursday.
"This is the start of the process of uncovering the truth, and other arrests will follow," MP Saad Hariri, the slain prime minister's son, told Radio-Orient from Paris.
The arrests have also ratcheted up the pressure on Lahoud, the Damascus protégé who himself has long denied allegations of complicity in the assassination and resisted pressure to stand down.
But Lahoud said: "Everybody is innocent before the law until proven guilty. If evidence shows they are guilty then they might be put on trial. No one was arrested and these people are only being questioned."
The three security chiefs had quit in the aftermath of the bomb blast that killed Hariri and another 19 people. But Hamdan, who was questioned by UN investigators in June and his house and office searched, has refused to step down.
The murder triggered massive opposition protests and heightened international pressure on Syria, which pulled its troops out of the country in April after a three-decade military presence.
Legislative elections were held in May and June, which for the first time saw anti-Syrian politicians dominate parliament.
Since the Hariri attack there have been 11 bomb blasts in Lebanon and several anti-Syrians including a politician and a journalist have been killed. A number of prominent figures, including Saad Hariri, now spend much of their time outside the country for fear of assassination.
© 2005 Agence France-Presse
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