A Kenyan foreign ministry official said on Thursday the accord would not be a final peace deal to end Africa's longest-running civil war.
The official said a final, formal peace agreement would be signed "sometime in the New Year, probably in January".
There was no immediate comment from the Khartoum government and the southern rebel Sudan People's Liberation Movement (SPLM).
Their peace process has been built on a series of protocols confirming agreement on a variety of contentious issues such as wealth- and power-sharing.
"There will be a signing ceremony tomorrow 31 December 2004 at the Sudan Peace Talks between the two parties, namely the Sudan government and the SPLM namely (a) Implementation Modalities and (b) Agreement on a Permanent Ceasefire," a Kenya Foreign Ministry statement said on Thursday.
Such an agreement would not cover a separate war raging in Sudan's western Darfur region.
Officials of the Khartoum government and the SPLM have pledged to sign a final peace by the end of the year to end a 21-year-old war that has killed an estimated two million people, mainly through famine and disease.
Sudan First Vice President Ali Osman Taha and John Garang, leader of the Sudan People's Liberation Army (SPLA), were meeting in the Kenyan town of Naivasha for the talks.
Millions have died, mainly due to
famine and disease, in the south
During an extraordinary meeting of the UN Security Council in Nairobi last month, the two men pledged to sign a final pact by 31 December, which is also the date the current ceasefire ends.
Observers to the negotiations have said that, barring major progress, any agreements announced by Friday's deadline would be piecemeal and more an exercise in face-saving for the parties.
Sudan and the rebels have so far signed accords on security arrangements, the sharing of power and wealth, and the status of three disputed periods during the six-year interim period.