KHARTOUM, SUDAN -- Libya has emerged as Sudan's major arms supplier less than three years after fulfilling the same function for southern-led insurgents trying to overthrow the Khartoum regime, according to diplomats and Sudanese officials.

Sudanese officials say that their country is hard-pressed and has no choice but to accept Libyan help. But they worry that Libyan leader Col. Moammar Gadhafi's principal objective is to buy influence and subvert government authority in the province of Northern Darfur, which abuts both the Libya and Chad borders, to win a freer hand in pursuing his war against Chad.

Combined with lawlessness, civil war, and a moribund economy, the growing sense of drift symbolized by the government's toleration of rising Libyan influence has weakened faith in the ability of Sudan to surmount its troubles independently, according to diplomats and Sudanese officials.

Originally, Libyan backing for the Ethiopia-based Sudan People's Liberation Movement, led by American-educated John Garang, reflected the deep personal animosity between Gadhafi and then-president Jaafar Nimeri, who ruled from 1969 until his overthrow by a civilian-led popular uprising in April 1985.

Military cooperation between Khartoum and Tripoli began after Nimeri's ouster, during a year-long transition from military to civilian rule. It blossomed in 1986 when Sadiq Mahdi, who spent years in exile in Libya, won the first elections in a generation and became prime minister at the head of a coalition government.

"We need help, and Libya provides oil, weapons and ammunition," one senior Sudanese official said.

Libya openly has provided Sudan's Air Force with Soviet-built MiG23 fighters and on occasion has loaned Tu16 bombers and other relatively sophisticated hardware to help the government combat the five-year-old insurgency.

Iraq, Jordan and the Persian Gulf's Arab states also sent arms and ammunition after Garang's forces, consisting largely of animists and southern Christians, for the first time briefly occupied two towns just inside the Moslem north last November.

But western diplomats are concerned about the thousands of Libyan arms readily available in desolate and famine-stricken Northern Darfur and other arms smuggled across southern Sudan from Ethiopia or sold from surplus stocks accumulated during Chad's two decades of strife.

In Northern Darfur, 800 to 900 members of Gadhafi's Islamic Legion cross the border at will, ostensibly bringing relief supplies but often under escort by Libyan Army vehicles, according to diplomats. In Southern Darfur, equal numbers of Chadian rebel forces conduct raids into their homeland, and Chadian regular Army units sometimes cross hundreds of miles into Sudan in hot pursuit, they added.

"It's no longer tribesmen with old rifles rustling cattle and stealing women, but bandits in Toyota pickups armed with machine guns," remarked a European diplomat about the lawlessness that, according to Interior Ministry statistics, took at least 159 lives in 1987.

"All this muddies the waters wonderfully for Gadhafi if and when he wants to move against Chad in a big way," the diplomat said.

Other indications of Libyan influence include a recent statement by a leader of the Democratic Unionist Party, which has traditionally been anti-Libyan, backing Gadhafi's claims to the contested Aozou strip along the border with Chad.

Airport visas were issued recently to 15 Libyans at the insistence of a minister belonging to Mahdi's Umma Party, so the Libyans could participate in a recent congress here of Gadhafi-financed "popular committees."

The committees are based on the same concept as those that make up Libya's decentralized administration.

The Libyans' participation in the committee meetings was in apparent defiance of a Sudanese government ban on foreigners' attendance at local political functions.

The ban was ordered after the assassination Jan. 17 of Mehdi Hakim, a prominent Iraqi exile whose brother runs an Iran-based Shiite Moslem organization that is opposed to Iraqi President Saddam Hussein.