To the distress of U.S. government officials, Libya's Muammar Qaddafi appears on the verge of winning the first significant military victory outside his own borders. Some 3,000 of his troops are wresting it for him in the little African country of Chad on Libya's southern border.

"After all those fiascos," one government specialist on the Chad conflict said yesterday, "it looks like the colonel is finally going to win one." He added that Libya's display of force has sent shudders through neighboring African countries but has been largely eclipsed in western capitals by news of Iran-Iraq and Afghanistan.

Even though Qaddafi has sent troops and armor deep inside Chad and is launching air attacks from three different air fields within the country, this big military presence is difficult for other African countries to condemn because, officials said, the mercurial Qaddafi, a radical who constantly assails the United States, is fighting on the side of the coalition backed by the Organization of African Unity.

Leader of that coalition is Chad's president, Goukouni Queddei, who is being challenged in Chad's 16-year old civil war by Hissene Habre, former defense minister.

Although they admit their intelligence from Chad is scanty these days, U.S. officials said they feel their information is solid on these points:

Between 3,000 and 3,500 Libyan troops are deep inside Chad, along with a thin line holding the strip of Chad border territory Qaddafi annexed before throwing his weight on Goukouni's side.

Libyan planes -- including Soviet supplied SF260 fighters, U.S. C130 transports and commercial airlines -- have been mobilized to help Goukouni. Libya is using three different fields inside Chad: Aozi in the north, Fada in the center of the country and one north of Ndjamena, the capital.

Libyan weaponry, advanced by African standards, is battering the Chad capital with no attempt to minimize civilian casualties. Deadly Stalin organ rocket launchers, artillery and fighter planes all have been used.

About 500 Libyan troops are among those poised outside Ndjamena for a big push to take the capital. The push could start without the West detecting it right away, because intelligence on tactical moves is so slow in coming, officials said.

Beyond those points, the speculation about Qaddafi's motives begin. U.S. officials said they believe Qaddafi sees his seemingly decisive intervention as a way to control events in Chad if the coalitin wins. Also, these officials said, Qaddafi could use Chad as a staging area for thrusts against other lightly defended states.

"The Sudan and Niger," said one defense official about those two countries on Chad's border, "are waking up to this danger."

Acknowledging that Qaddafi's intervention in Chad's civil war does not affect any "direct" U.S. interests, one government specialist on the conflict said the Libyan leader's strengthened hand endangers the fragil political fabric of central Africa.

In this regard, he said, Senegal's recent call for the Organization of African Unity to assess the situation in Chad is encouraging.

U.S. officials interviewed declined to be quoted by name. But at the same time they were anxious to alert the public and other world capitals to what they regard as the extensive and potentially destabilizing intervention of Qaddafi into Chad.

In a related development yesterday, French Foreign Minister Jean Francois-Poncet said in Paris that he was "concerned" about reports of the "intervention of foreign elements coming from Libya" in Chad. France withdrew its military forces from Chad in May, two months after the current fighting there broke out. Francois-Poncet declined to say, when asked, if France would send troops back into Chad. He said he did not want to "prejudge" any requests for such help Chad's neighboring countries might make.