China, after a fresh warning of potential trouble along the disputed Sino-Soviet border, has reported two incidents along the border with Outer Mongolia, where large numbers of Soviet troops are stationed.

In one incident, China said it captured a saboteur carrying explosives and "attempting to create border incidents" in Kirin Province, which borders on Mongolia.

The other involved the interception of a motorized reconnaissance patrol from Mongolia in the Gobi Desert. There was no indication whether the patrol insisted of Mongolian or Soviet troops. The Chinese referred to it only as "the enemy."

The Chinese have not reported any incidents along the border with Mongolia for several years. There have been sporadic reports of minor incidents along the frontier with the Soviet Union.

In Moscow today, the official Soviet news agency Tass called the reports "sheer concoction" and said, "Its authors are obviously engaged in wishful thinking."

Both incidents were reported by Peking Radio Sunday. A translation of the monitored broadcast was obtained yesterday.

A day earlier, Chinese broadcasts said "a grave danger" of Soviet "subversion and aggression" prevailed along the Sino-Soviet border and reported that an army unit had been commended for foiling "abnormal activities" by Soviet personnel.

The Chinese radio gave no details of those "abnormal activities," but did say they occurred on the Heilungkiang, or Amur River, which separates the two countries.

The report on the arrest of the saboteur with high explosives said he was discovered by a two-man border patrol team. While one member of the patrol went to summon help, the other, Kiu Ko-pin, gave chase.

After catching the suspect, a Chinese described as "a robber and a criminal," Liu fought with him, subduing the suspect and tying him up.

"Through interrogation, the man was found to be a speculator from another place and also a robber and a criminal attempting to create border incidents, who was wanted by the county public security bureau," the report said.

He was carrying "more than 130 detonators, 4 kilograms (8.8 pounds) of explosives and a bunch of fuses," Peking Radio reported.

In the other incident, Peking Radio said a Chinese army cavalry unit, patrolling with guard dogs in Inner Mongolia's Gobi Desert, spotted a cloud of dust in the distance.

Upon investigation, they found "an enemy motor vehicle. . . trying to sneak into our territory when some sneaky persons tried to alight from the vehicle and scout our territory."

When the Chinese soldiers appeared, Peking Radio said, "these people panicked, returned to their vehicle and drove away. . . The enemy's plots were foiled."