BALTIMORE, SEPT. 14 -- The Maryland Commission on Human Relations reported a marked increase today in incidents of racial, religious and ethnic violence and prejudice in the state in the last four years.

Commission statistics showed incidents of assault, arson, cross burnings, vandalism and threats reported by police across Maryland jumped from 398 in 1986 to 686 in 1989.

A Maryland State Police official cautioned that while there has been a real rise, much of the increase can also be attributed to improved reporting procedures by police and greater public awareness of a phenomenon that for years has gone largely unreported.

"In the last two years, we've done quite a bit in educating law enforcement agencies and making the public more aware of the need" to report so-called hate incidents, said Capt. John Cook, chief of the State Police intelligence unit.

Public awareness programs have included distribution of thousands of brochures and pamphlets to churches, schools and community groups.

Jennifer Burdick, executive director of the Human Relations Commission, agreed that some of the increase is due to improved reporting, especially in Maryland's rural counties.

But she said in suburban jurisdictions, such as Montgomery, Howard and Baltimore counties, where reporting traditionally has been good, "they've experienced real increases."

The commission report shows, for example, that the number of incidents in Montgomery County jumped from 108 in 1988 to 131 in 1989, and in Howard County from 32 in 1988 to 45 in 1989.

Both the NAACP and the Anti-Defamation League of B'nai B'rith, which monitors antisemitic acts, said the report reflects their own findings.

"We have seen a marked increase, both nationally and locally," said David Friedman, director of the Washington-Maryland-Northern Virginia region of the Anti-Defamation League.

Incidents have ranged from assaults on Jews to vandalism of synagogues, according to Friedman.

Mira Boland, Washington fact-finding director for the league, said much of the activity is attributable to loosely organized neo-Nazi skinhead groups.

Leroy Mobley, Maryland regional NAACP director, said blacks have experienced a "new virulence in hostility" in recent years.

Windows at NAACP national headquarters in Baltimore were shot out last summer and the building was picketed by skinhead and Ku Klux Klan activists in January.

"I don't know what accounts for this," said Mobley, "but it could be the widening of the gap between blacks and whites, between the haves and have-nots."

The commission report shows 505 incidents throughout the state in 1982, the first year the commission collected data under a new state law. After that, the totals fell to between 300 and 400 annually, then shot up to 546 in 1988 and 686 in 1989.

A high percentage of the 1989 incidents -- 645 of them -- were reported in the state's most populous areas: Baltimore City and Montgomery, Prince George's, Howard, Anne Arundel and Baltimore counties.

The report shows the bulk of the incidents statewide were assaults and vandalism, 206 of the former, 163 of the latter.

Twelve cross burnings were reported. The report classified 82 percent of the incidents as racial and the remainder as religious or ethnic.