NEW YORK (AP) _ Public television's ''The MacNeil-Lehrer NewsHour'' features more whites and males and is more government-oriented and conservative than ABC's ''Nightline,'' says a group that studied both shows.

The assertion was made by a liberal media watchdog group, Fairness & Accuracy in Reporting, in a study released Sunday. FAIR president Jeff Cohen said that the PBS show has a ''narrow, pro-establishment guest list'' that ''mocks the original mandate of public television'' to provide diversity.

''NewsHour'' executive producer Les Crystal said the news program agrees that diversity is important ''and we clearly feel we can and should do better in that regard.''

But he disputed what he called FAIR's contention that the show doesn't criticize the government much and asks one-sided questions.

''That's just not true,'' he said Friday. ''We look for differing points of view and have them on almost all the time.''

The FAIR study of ''NewsHour'' broadcasts from Feb. 6 to Aug. 4, 1989, was conducted by Boston College sociologists William Hoynes and David Croteau, who made a study critical of ''Nightline'' last year.

The ''Nightline''' report, examining 40 months of the ABC program from 1985 to 1988, found that 89 percent of its guests were men, 92 percent were white, and that conservative leaders were the show's most frequent guests.

FAIR's new study, entitled ''All the Usual Suspects: MacNeil-Lehrer and Nightline,'' also compared ABC's program with ''NewsHour'' during the same six-month period the latter was studied.

The two professors making the study found that ABC's show has slightly broadened its guest list since the original study, but that ''our hopes for significant change were not met.''

Their ''NewsHour'' study found that of U.S. citizens appearing as guests, 90 percent of them were white and 87 percent were male. The figures rose on programs about international politics, it said, with 94 percent of U.S. citizens appearing to discuss world politics were both white and male.

The study offered no racial or gender percentages for guests who were not U.S. citizens.

It characterized as ''more representative'' the guests invited when the show's topic was domestic politics. It said that 26 percent of them were women, but gave no figures on the race of female guests.

FAIR's study said the show's guest list was dominated by two conservative Washington think tanks, with a total of 14 guests provided by the Center for Strategic and International Studies and the American Enterprise Institute.