The Sudanese chief of security charged today that Libya intends to overthrow President Jaafar Nimeri's government through sabotage, assassinations and a two-pronged attack across the Libyan and Chadian borders.

Minister of Security and Vice President Omer Mohammed Tayeb drew an elaborate scenario of alleged subversion in giving the first details to support Nimeri's claim that Libya is planning to invade.

Although Western diplomats are dubious about Libya's ability to mount an invasion across hundreds of miles of desert, the United States has pledged to accelerate delivery of $100 million of military equipment to Nimeri.

He said Libyan leader Muammar Qaddafi originally intended to carry out the invasion plan this month but had to call it off because officials discovered the plot when thousands of Sudanese, many returning from Libya, were arrested last month.

"Thank heaven we have done that," he said, adding that otherwise Nimeri would have been assassinated. "They have postponed now because they think we are ready," he said. "But they will try again. There has been a decision by Qaddafi to overthrow this government. When and how to do it is left to the circumstances. This is a series of plots."

Gen. Tayeb told reporters that Libya had started concentrating troops on its border with Sudan two weeks ago, before the assassination of Sudan's ally, Egyptian president Anwar Sadat.

The main attack, Tayeb said, would be on Khartoum, using agents infiltrated into the city and Sudanese irregulars who would drive in special desert vehicles from the Libyan border, 600 miles northwest of here.

A second front would be opened by Libyan-trained Sudanese and Qaddafi's own forces crossing from Chad and occupying western Sudan. The attack would be accompanied by assassinations of 20 or 30 key officials, he said.

If that succeeded, "it is finished," Tayeb said. "After that they can make the linkup with Libyan troops in four hours," using paratroopers and an airlift to forestall possible Egyptian or U.S. assistance.

"People said the Libyans would never go to Chad," referring to the more than 5,000 Libyan troops now in that neighboring country as the result of a civil war. "But they did. The leaders of Africa were sleeping."

Tayeb declined to disclose how many Sudanese are being detained but said in the last two or three months 11,000 Sudanese had returned from jobs in Libya.

The Egyptian Middle East News Agency said today that 1,366 people were arrested Friday in Sudan and that another 6,000 to 7,000 suspects were being questioned about involvement in a plot to undermine the Numeri government, United Press International reported. "Some are honest; some we should suspect," Tayeb said of those returning from Libya. Interrogations of the prisoners had revealed that there were 10 or 15 ringleaders who came to set up revolutionary committees as in Libya, he maintained.