Libyan border activity sends mixed messages to Chad, West. INTERPRETING QADDAFI

The African country of Chad is sounding the alarm - ``Libya is preparing to renew hostilities against us.'' Mahamat Ali Adoum, Chad's ambassador to Washington, says his government is bracing for an attack, after five months of a tenuous cease-fire in the fighting. The Libyan thrust, he says, could come before the planned April summit meeting of African leaders trying to mediate the dispute over the Aozou Strip, which separates Chad and Libya.

US officials say they are carefully watching the situation. Libya has undertaken a major buildup of its forces along the disputed border since last fall's cease-fire, say US and French experts on Africa. In recent days, Libya has apparently reinforced its several thousand troops operating in western Sudan on Chad's eastern border, according to intelligence reaching Washington.

Western experts are not certain Libya intends to launch an offensive, however. Some say they think the buildup is mainly to prevent further embarrassing Libyan losses in defending the disputed areas, or to serve as a basis for raids on Chad by ``dissidents.''

Chad's leadership believes the signs are clear, says Ambassador Adoum: Libya's Col. Muammar Qaddafi is determined to regain face and influence after the string of defeats that Chad's Army inflicted while driving Libyan troops out of northern Chad last year.

The April summit will aim at avoiding new hostilities. Current diplomatic speculation is that the seven African heads of state selected by the Organization of African Unity (OAU) to resolve the dispute will not come down clearly in favor of one side, but will try to get Chad and Libya to agree to some type of international judicial arbitration of conflicting claims to the Aozou area. Observers, however, agree that hostilities could be renewed if the diplomacy becomes bogged down, and they are worried about reports that the summit might be delayed.

Adoum says Colonel Qaddafi is just playing for time while preparing an attack. Chad's Army, however, is short on the kind of defensive weapons needed to blunt a Libyan offensive, he says. Western specialists agree Chad's forces are outgunned but say they are superb in mobile desert warfare.

Chad is taking defensive measures apparently aimed at slowing a Libyan attack, US officials say, which have convinced the officials of the sincerity of Chad's concerns. But Western intelligence analysts, specialists, and diplomats are divided over Libya's intentions and capabilities.

Sources agree, however, that Libya is bolstering its five military bases nearest Chad. Libya's armor presence in the area has reportedly tripled since September, while fortifications and gun emplacements have been added. In addition, it is completing enlargement of an airstrip at a base in Tuomo, seven kilometers inside neighboring Niger, which could provide Libya's Air Force extended capabilities over Chad, sources say.

Libya continues regular overflights of Chadian territory, in violation of the OAU-arranged truce, they say. It has also concentrated its several thousand mercenary troops from Lebanon, Yemen, and elsewhere at southern bases. These troops are considered more effective in close combat than Libyan forces.

Libya has more than 10,000 troops in the south, sources agree, and 2,000 to 3,000 Libyans and Chadian dissidents in western Sudan. Libya has reportedly moved up to 2,000 more troops into the Sudan recently, according to Western intelligence sources. These Libyan troops keep a large number of Chadian forces from moving to the disputed Aozou Strip. According to Adoum, the troops in Sudan make periodic incursions into Chad, and Chad pursues them across the border.

On the other side of the ledger, a number of official and nonofficial specialists, among them Henry Schuler of the Center for Strategic and International Studies in Washington, say Libya is far from ready for an offensive. Troop morale, logistics, and training are just too poor for sustained attacks, these specialists say.

Libya does not have the trained manpower in place to attack with its reinforced armor, say some Western intelligence sources, nor has it yet begun the offensive training patterns or the logistical preparations expected before an offensive. Other sources say Libya's Lebanese mercenaries are reportedly unhappy and have clashed at least twice with local troops.

Nevertheless, US officials continue to worry about Qaddafi's intentions. Libya received chemical weapons from Iran last year, they say, some of which are believed to be stored at Matan as Sarra near Chad. US officials suspect Libya is building a chemical-weapons production facility in the south disguised as a petro-chemical plant.

The Reagan administration is currently reviewing its defense assistance for Chad to identify priorities for the year ahead, officials say. Chad is reportedly urging additional deliveries of sophisticated US anti-armor TOW and antiaircraft Stinger missiles. But Washington has a smaller aid pie this year for Africa.

On the diplomatic front, in preparation for the April summit, the foreign ministers of the OAU mediation group met last month to examine the reports of OAU experts who have studied the two countries' claims to the Aozou Strip.

Libya reportedly produced a 1973 letter from the then-President of Chad ceding the strip to Libya in return for financial and political aid.

Chad, on the other hand, bases its claim on the African principle, accepted since 1964, that borders recognized at the time of independence are inviolable. Thus, even if the former President did secretly made a deal, Chad maintains, it is not legal.

The problem for OAU, says a Western diplomat, is that even though the African mediators support the maintenance of independent borders, they are very hesitant to take on Qaddafi. The key, he adds, is to find a solution that both sides can accept, so the fighting will not just erupt again.