America's black television actors get more screen time than other minorities but their roles tend to be restricted to comedies, a study has found.

Black characters were more likely to appear in US comedies, with 39% of all black characters in situation comedies compared to 31% for whites, 23% for Hispanics and 21% for Asians.

One of the least-watched US TV networks, UPN, featured the most black characters, the study from the University of California, Los Angeles (UCLA), found.

Despite the large number of African Americans on television, they continue to be 'ghetto-ised'

UCLA study

Black actors made up 28% of the characters on UPN series, compared to about 12% on other networks.

More than half of all black characters who appeared on the screen for more than 10 minutes per hour of programming were on UPN and most appeared on two nights, Monday and Saturday.

Saturday is the least-watched night on American television.

CBS was the network with the second-largest percentage of all African-American characters at 17%.

"Despite the large number of African-Americans on television, they continue to be 'ghetto-ised'," the study concluded.

Other groups

But other minorities were in a worse situation, the study found.

Black and white characters represented 92% of all prime-time characters in the study but constitute only 82% of the US population, it said.

Hispanics were the most under-represented group in prime-time television, making up only 2% of all characters, although they make up 12.5% of the US population.

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Asian-Americans comprised about 3% of all characters, and American Indians were "invisible", according to the report.

"We are very proud of our record of diversity on air," said Paul McGuire, a spokesman for the WB Network.

He pointed out that WB will air a new Hispanic family sitcom next autumn, Greetings from Tucson.

The networks have been under pressure from civil rights group in America since 1999, when a clutch of new shows were perceived as mostly white.

But there has been little movement towards better ethnic diversity, said Darnell Hunt, the study's author.

Great anticipation

"Much of the promise of change on behalf of the networks has been lip service to appease people," said Hunt, director of the UCLA Center for African American Studies.

"There's been all this anticipation of change and there has been very little.

"Most of the networks have thrown out a few symbolic gestures and left most of the programming practices intact."

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While nearly all TV was multi-racial, ethnic characters usually appeared only as background "props" of little relevance to the story, the study found.

Mr Hunt, the author of a 2000 Screen Actors Guild study with similar findings, said progress has been hindered by white control of the entertainment industry.

"Minorities are even more under-represented in key behind-the-scenes creative and decision-making positions than they are on the screen," according to the UCLA study.

Researchers analysed 224 episodes of 85 comedies and dramas that were broadcast in October and November on ABC, CBS, NBC, Fox, UPN and WB.