President John Vorster, ending a six month silence about a growing scandal in the South African government, tonight denied allegations by a former top official that he approved a covert project to fund a progovernment newspaper.

His statement broke a strong tradition here under which the president, like the British monarchy, avoids public comment on political topics. Vorster, who formerly was prime minister, said he was making his remarks "in the interest of the truth." He indicated he was prompted to speak by allegations, which he called "the infamous lies," made by former information secretary Eschel Rhoodie on British television last night.

The fact that Vorster felt compelled to speak out seemed to indicate that suspicions about his role in funding The Citizen newspaper are being voiced even by loyalist government supporters as the scandal increasingly obssesses the government, headed by Prime Minister Pieter W. Botha since Vorster resigned to assume the largely ceremonial office of president.

The topic dominates newspapers, radoi broadcasts, conversations and debates in parliament as charges by Rhoodie and the opposition parties increase suspicions that there has been a cover-up of the full extent of the scandal.

Botha is attempting to avoid calling an election as a result of the scandal because of fears that a conservative faction within his National Party would gain the upper hand. This, in turn, could have important consequences on South Africa's policy on the continent's racial struggles, particularly in Namibia and Rhodesia.

Increasingly, however, it appears that new elections may be the only way out of Botha's political problems.

In an attempt to restore his administration's shaken credibility, Botha has urged the government probe team he appointed last October to take another look at whether any of his ministers knew of The Citizen or any other "irregularities" in the Information Department when Rhoodie ran it.

But opposition parties and even some progovernment Afrikans-language newspapers say this is not going to be enough.

The suspicions of a cover-up center on Vorster's role in The Citizen project. There are many who believe that the evidence heard by the government investigators, if released, would not support the official conclusions that Vorster did not know the paper was propped up with government money.

Rhoodie, who is wanted here on charges of fraud and theft, last night said that Vorster knew about the government's clandestine financing of the proapartheid Citizen newspaper, which Rhoodie set up to counter negative press coverage of the government. Although Rhoodie claims to have documents to prove his allegations, he has so far not revealed them.

In his statement tonight, Vorster, 63, reminded his audience that he had accepted responsibility for allocating the secret funds for a "propaganda war" against South Africa's opponents that was conducted by Rhoodie in the Information Department.

"But that does not mean I accept responsibility for how that money was used," Vosrter said.

In reply to the allegations by Roodie that Vorster knew about The Citizen project from its inception, Vorster said: "That is not true."