Soviet plainclothes security forces in the Afghan capital of Kabul, part of recently increased Soviet surveillance around Western embassies there, tackled a European-looking man who was running toward the gate of the U.S. Embassy last week, according to diplomatic sources here.

The diplomats said the man, described as fair-haired and wearing an unfashionable European-style suit for the type often seen in Eastern Europe, got out of a car about 100 yards from the American Embassy compound and began walking toward the gate. When he spotted security officers converging on him, he began running and was tackled about 20 yards from the embassy entrance, they said.

According to the report, received here today, the man was wrestled into a Soveity Army jeep that appeared almost immediately. Eyewitnesses were reported here as saying the Soviet security man in civilian clothes, who had been in front of the U.S. and other Western embassies in Kabul for days, first tried to stuff him into a car when they could not, they forced him backward into the Army jeep.

It was unclear whether the man was a Soviet soldier or civilian adviser from among the thousands of military men and experts posted in Afghanistan. The diplomatic sources said it was certain, however, that he was not an Afghan, who are virtually always dark-haired and swarthy. Based on the eyewitness accounts that they relayed, the diplomats also were certain that he was not a casual passer-by on the street being picked up on some criminal or political charge.

Furthermore, other Western embassies reported two recent occasions when European-looking men appeared at their gates only to be driven off by Soviet plainclothes security forces. The sources were unsure whether these incidents involved the same man.

According to reports received here, the Soviet recently have increased their security around embassies of Western nations considered unfriendly to the Soviet-installed government in Afghanistan.

At one point, according to a well-informed source, Soviets were stopping all nondiplomats from entering the American Embassy in Kabul. Afghans seeking U.S. visas were told by Soviet security guards that they could send their applications to the embassy, but not enter its grounds.

U.S. Mebassy officials protested to the Afghan Foreign Ministry, according to a source here, but the ban on visits to the American compound continued until after the man was tackled outside its gates.

Partly as a result, diplomats here speculated that Soviet authorities had received word that someone was trying to defect to the West and had added extra guards around the embassy to catch him.

For days before the man was tackled, according to diplomatic reports, Soviet plainclothesmen were seen all over the street in front of Western embassies. Eyewitnesses said when the man started heading for the American Embassy, other security guards leaped into the street from behind a wall across from the U.S. compound.