Sudanese President Jaafar Nimeri said yesterday that Muammar Qaddafi of Libya had offered his economically hard-pressed government $5 billion if he would sign a unity agreement similar to the one Qaddafi worked out with Morocco last September but that Nimeri had refused.

The Sudanese leader said in an interview with The Washington Post that the offer had come during talks the Sudanese ambassador in Paris held with a Qaddafi envoy several months ago.

"We refused, and we stopped talking with him," he said.

Nimeri said he thought Qaddafi was seeking through his offer to "get inside the Sudan" to make contact with the opposition there and to isolate his country from Egypt, which is linked in an economic integration accord with the Sudan.

"Because he was successful with Morocco, he wanted to use this [unity offer] with the Sudan," Nimeri said. "He wants to come into the integration agreement with Egypt and the Sudan . . . . We said 'no.' "

Nimeri said the Paris meeting with Qaddafi's envoy was "not a new thing" and was "the 10th time or the 12th time" it had happened.

"I don't send my people; Qaddafi is asking. He asks all the time that we send a man to talk and that we get our relations back to normal. I don't like to close doors and gates with him . . . . I always tell him my aim is peace.

"The last time, he said, 'I am going to pay $5 billion to you.' He thinks I am in need of money so that I will obey his instructions. He doesn't know that in the Sudan we have had worse famines before. We lost about half our population, but we didn't go to Libya."

Nimeri blamed most of the Sudan's current financial and economic woes on drought, which he said has reduced agricultural production to 10 percent of normal in many areas and brought over 1 million refugees into the Sudan from neighboring countries.

He pleaded with the Sudan's creditors and the International Monetary Fund to look upon his country as a "special case" and to give it "four or five" years to recover from the drought and pay its nearly $9 billion debt. He criticized the IMF, which he said has let him "fall down again to the bottom" and "broken my seat" by insisting the Sudan immediately pay $120 million in arrears.

European donors had delayed their aid, he said, though he said he was never aware that the United States had held back on $180 million in economic aid as a result of the Sudan's difficulties with the IMF.

Monday, President Reagan announced the resumption of the aid plus an additional 225,000 tons in emergency food relief.

Nimeri said that at the same time Qaddafi was offering him $5 billion to normalize relations, the Libyan was encouraging Libyan- and Ethiopian-backed rebels in the Sudan's southern provinces to seize a town and set up a government that Libya and Ethiopia could recognize.

He said 120 rebels of the Sudanese People's Liberation Army attacked Jekau, a town in eastern Upper Nile Province, 12 days ago in an attempt to take it over. An army garrison of 2,000 beat off the attack, however, and killed 200 rebels, Nimeri said.

He blamed troubles in Khartoum after recent food-price hikes on refugees and unemployed Sudanese from outside the city.

He said that 800 to 900 of them were put on a train and taken outside the capital, but that about 200 Moslem Brotherhood members, whom he accused of sparking the trouble, are still being held.

"Their intention is to rule the country, and if they have control . . . this will be another Iran," he said.