Libyan leader Muammar Qaddafi, his economy weakened, his foreign adventures faltering and his alliances showing signs of strain, now faces increasingly coordinated pressure from his North African neighbors.

According to western diplomats and Arab officials here, as well as recent press reports from Tripoli, the Libyan capital, Qaddafi now finds himself more vulnerable and isolated than he has been in years.

Egyptian President Hosni Mubarak's national security adviser, Osama Baz, visited Tunisia Oct. 9 to explore the establishment of a "confrontation front" against Qaddafi, according to reports in the Arab press. On Nov. 4, Tunisian envoy Habib Chatti and Abdel Qadr Belcassem, a senior adviser to Algeria's president, were in Cairo to discuss recent developments.

"The commonality of interests is defined, and coordination is taking place," one well-informed western diplomat said this week.

"I think Qaddafi is even more afraid of the Algerians than he is of the Egyptians," he continued. "If you're Qaddafi sitting between these pincers, you've got to be nervous about it."

Last month the Algerians moved troops conspicuously near the Libyan-Tunisian borders, according to a Reuter report from Tripoli, and Qaddafi pulled his own forces back 25 miles from the desert frontier for fear that the Algerians were looking for a pretext to attack.

This comes amid several press reports that this fall President Reagan authorized the CIA to carry out covert operations to undermine Qaddafi by assisting neighboring states that would like to see Qaddafi removed.

While some of Qaddafi's problems have been developing gradually, the catalyst for his current predicament appears to have been his decision last summer to expel thousands of foreign workers that his economy, debilitated by dropping oil prices, could no longer sustain.

By ousting about 30,000 Tunisians and 10,000 Egyptians and threatening to expel still more, he reduced the leverage he once held with those neighbors and gave them an incentive to work together against him.

Tunis severed diplomatic relations with Tripoli on Sept. 26 as a direct result of the expulsions.

At the same time, Algeria moved forcefully to back Tunisia's stand. Algerian President Chadli Bendjedid visited Tunis in a public show of support at the height of the crisis in September.

Tunisia and Algeria then began their high-level diplomatic contacts with Egypt, which previously had been kept at a diplomatic distance because of its relations with Israel.

The United States, which vehemently opposes Qaddafi for supporting terrorist operations and anti-U.S. guerrilla movements, has maintained a low public profile through the recent developments.

Publicly, both Algeria and Tunisia have condemned any CIA effort to oust Qaddafi, and Egyptian officials express skepticism at press reports of such a plot.

Libyans close to Qaddafi told Reuter this month they viewed the story as a propaganda ploy by the Reagan administration similar to several almost "seasonal" campaigns against Qaddafi in the past.

But Qaddafi's immediate reaction has been one of caution. Not only did he pull his troops back from any possible confrontation, but he sent a special envoy to congratulate Algeria on the anniversary of its revolution.

This week, top Libyan officials met with representatives of Iraq and the Palestine Liberation Organization in an Arab League-sponsored effort to reduce bitter differences between them.

Yet the pressure on Qaddafi from other fronts and the fallout from his past adventures appears to continue unabated:

*The one opportunity recently afforded Qaddafi to expand his influence is in Sudan, where his bitter foe, president Jafaar Nimeri, was deposed in April. Qaddafi has stated publicly his desire to win the new Sudanese leaders away from Egypt's influence.

But after some initial openings to Qaddafi and the establishment of a loosely structured Libyan-Sudanese military protocol during the summer, in the last few months Sudan's leaders once again publicly warmed to Cairo with a series of high-level visits here in late September and early October.

*Until late in the spring, Libya appeared to have forged a close working relationship with Syria and Iran. But that alliance now seems to be in considerable disarray.

Qaddafi publicly opposed Syrian-backed attacks on Palestinians in Lebanon, and Syrian President Hafez Assad has entered a process of highly visible rapprochement with Jordan's moderate King Hussein.

Reports in the Arab press also suggest that Assad's relations with Tehran have been soured because of Iran's persistent involvement with Shiite fundamentalists in Lebanon who oppose the kind of secular regime Assad wants to see in Lebanon.

*Despite a recent visit to Moscow, Qaddafi's relations with the Soviet Union also are reported to be strained.

According to accounts by western reporters in Tripoli, the Soviets have refused to sell Qaddafi sophisticated MiG29 fighter aircraft or SA5 missiles and are demanding payment of his military debts -- estimated at more than $5 billion -- in cash.

*In Chad, President Hissene Habre has received new diplomatic and possibly material support in his fight against Libyan-backed rebels from both Egypt and Algeria, according to western diplomats here.

Qaddafi claims to maintain only a few Libyan advisers in Chad to help the forces of rebel leader Goukouni Oueddei. But diplomats in Tripoli reportedly estimate a presence of about 5,000 Libyan troops there and suggest that the Chadian war is increasingly unpopular with Qaddafi's military commanders.

*Even on the terrorist front, Qaddafi has been subjected to a series of embarrassments during the past year, especially at the hands of the Egyptians.

Earlier this month, his latest effort to carry out an operation inside Egypt was thwarted by Mubarak's security forces and reduced to the level of comic opera in its presentation to the public.

Superimposed on a picture of bloody hand prints, Egyptian television titled its news special on the event "Terrorism: Failed Attempt No. 4."

The program reviewed Qaddafi's ill-fated fourth attempt to have Libyan ex-prime minister Abdul Hamid Backoush assassinated here a year ago, a plot to bomb the U.S. Embassy in May and his foiled attempt to eliminate other exiles in August.

Yet the ultimate effect of such humiliations and pressures on Qaddafi's 16-year-old government remains a question that few observers answer with any confidence.

One Egyptian source with extensive military and intelligence contacts suggested that Mubarak is ready to invade Libya if any of Qaddafi's exploits here should move from the realm of comedy to tragedy at the cost of Egyptian lives.

"If they succeed in killing one Egyptian or destroying some sort of installation or establishment here, I assure you this means war," said this source. "This is the green light."

But western diplomats said they doubted that Mubarak would take such drastic action against any but the most flagrant provocations.

Backoush said in an interview this week that no exile group he knows of has a presence in Libya sufficient to topple Qaddafi, who is obsessed with security.

Echoing a view held by many analysts, Backoush suggested that only "through the Army" will Qaddafi be overthrown "eventually."

But according to well-informed sources here, an Egyptian report in September of a Libyan mutiny remains completely unconfirmed and was probably a fabrication. It may, however, point to the hopes now held by Qaddafi's enemies.

The Egyptian semiofficial newspaper Al Ahram reported that a group of officers had refused Qaddafi's order to prepare for an invasion of Tunisia and instead tried to bomb him in his headquarters.

The implied hope is that, given his current weakness, the threat of an imminent war with Tunisia and Algeria on one front or Egypt on the other could spark a rebellion in the Libyan Army and bring Qaddafi down without a full-scale invasion or an externally directed plot to eliminate him.