Mayor Marion Barry injected himself last night directly into attempts to lower the District of Columbia's strikingly high infant mortality rate by saying he would mediate any disputes between the city's Department of Human Resources and his newly appointed committee studying infant mortality.

The eight-member committee met for the first time last night with DHR health leaders and the mayor. According to committee chairman Dr. Fredrick Green, Barry told the committee that "if there is a major dispute between the committee and DHR, the mayor will be informed of it and the mayor will arbitrate."

According to Green, DHR's plan to lower the nation's highest big-city infant mortality rate is "deficient in many ways," particularly in not drawing more heavily on the private medical sector for assistance.

"One of the issues that really concerns us is that we are reacting to 1977 data," said Green, who pointed out that the most recent mortality statistics compiled by DHR are that old. "We can't wait until next year to find out what happened last year," he said. "We should know about 1978 in two or three months."

Green said that Barry, who joined the committee for one hour of its three-hour first session, "wants results within this year."

Green said the committee must launch a media campaign to give the infant mortality problem wider attention. "I would like to see something like 'save the babies' on the lips of everybody by the end of the year," he said.