Two incidents of vandalism and a cross-burning directed at black families in suburban Maryland were reported by police last weekend.

Prince George's County fire officials said a wooden cross was ignited and placed against a car belonging to James Herring, in front of Herring's home on Fontana Drive in Lanham early yesterday.

Fire officials estimated the damage to the car at $800 to $1,000. No one was injured.

In Wheaton, vandals broke into the Allen Chapel AME Church at Dayton and Dodson lanes sometime Saturday night or Sunday morning, wrote "KKK" and drew a swastika on the walls inside the building with a felt-tip marker, Montgomery County Police reported.

The intruders also scrawled the words, "You are all going to die," police said.

In Gaithersburg, police reported that the letters "KKK" were sprayed on a car belonging to Merlee Lancaster in front of her home on Suffolk Terrace early Saturday.

No arrests have been made in any of the incidents, police said.

Officials speculated that the incidents may have been a reaction to the Martin Luther King commemorative march in Washington on Saturday.

Despite the weekend activity, the total number of incidents of vandalism or violence directed at either blacks or whites in Montgomery and Prince George's counties has declined so far this year compared with the same period last year, police said.

There were 74 such incidents in Montgomery County between Jan. 1 and July 31 this year, compared with 91 for the same period last year, police said. But of those totals, the number of racially motivated assaults jumped from 16 to 36, police said.

Sgt. Richard Williams of the police department's community relations branch said the assaults were "almost exclusively blacks against whites or whites against blacks" with the vandalism incidents directed mainly against Jewish properties or homes.

"I'm really puzzled by the pattern ," Williams said.

He said the incidents are not confined to any one area but "seem to be happening all over the county. Tolerance is just becoming shorter and shorter."

In Prince George's County, the number of reported incidents, including assaults, harassment and vandalism, decreased from 43 in the first six months of 1982 to 39 in the first six months of this year, according to Bill Welch, executive director of the county's Human Relations Commission. Cross-burnings decreased from six to four in the same period, he said.

Williams and Welch said the Saturday march commemorating the 20th anniversary of King's historic march on Washington for civil rights may have provoked the weekend incidents. "I wouldn't rule out the march," which drew an estimated 300,000 participants, Welch said, "but then again, if someone was just responding to the march, he or she probably would have done something much more controversial or spectacular."

George Powell, president of the Allen Chapel AME Church board of trustees, said the swastika and "KKK" letters marked the second time in four months that the church has been vandalized. Last time, he said, vandals wrote "KKK" and racial slurs on the outside of the building.

Powell said the earlier incident was not reported to police. "We just cleaned it up," he said.