President Reagan's black supporters, in and out of government, are growing more that slightly embarrassed over the slow pace of black appointments.

The official word from the White House is not to make any judgments until the administration's staffing is complete. And, officially, the black supporters of the administration aren't making judgments. Unofficially, however, they are growing very nervous.

I've just seen a letter from William O. Walker, publisher of the Call and Post newspapers of Ohio, to members to the Reagan-Bush Campaign.

Walker, who signs himself as temporary co-chairman, raised the question of the group's continued existence. Then:

"Unfortunately, efforts to establish meaningful contacts with members of the Reagan team have been most discouraging. They neither return phone calls nor answer letters. Plus the fact that appointments of blacks are moving at a slow pace, if at all."

The Cleveland publisher called an informal meeting of his committee when he was last week for the annual convention of the National Newspaper Publishers Association.

And while he declined to discuss the details of his committee meeting -- indeed he seemed embarrassed that a reporter had known about it -- he made clear his disappointment both over access and the pace of appointments.

Nor is he alone in his disappointment. A number of blacks who worked for the Reagan-Bush campaign, including some who have taken jobs in the new government, are getting antsy.

One Reagan appointee said he was prepared for criticism from the black community for the very act of supporting a conservative Republican candidate but took the position that, once blacks saw how a conservative administration could work in their interest, the criticism would evaporate.

"But I have to say I'm getting concerned," he said. "If there is no clear signal soon, a lot of us may stand the risk of losing credibility."

A black member of the Carter administration, perhaps not surprisingly, agreed.

"The assistant secretaryships are important, of course," he said, "but the key questions is: Who is on the domestic policy staff and on the national security staff? The thing about serving at that level is that you are in position to know and influence what the hell is going on. I'm talking about input from the start, not after a policy has been announced."

Is any black in that position with Reagan?

"If Mel Bradley is, he's the only one," the Carter man said.

Bradley is one of fewer than a dozen senior policy advisers on the White House staff, which makes him, aside from HUD Secretary Samuel Pierce, the most influential black in the administration.

After those two, the list is pretty short in both numbers and influence: Former D.C. school superintendent Vincent Reed is an assistant secretary of the Department of Education, slated by Reagan to be abolished. Arthur Teele heads the Transportation Department's Urban Mass Transit Administration; Thad Garrett is domestic adviser to the vice president; Thelma Duggin, a White House special assistant for political liaison has responsibility for black affairs, youth and volunteers; Rosslee Green Douglas is director of the office of minority economic impact for the Department of Energy, also ticketed by Reagan for oblivion, and Ricardo Urbana, a black Hispanic from Howard University, has been named judge of the D.C. Superior Court.

Karna Small, White House press aide, repeats the familiar warning not to reach any premature conclusions about the Reagan appointments, And, indeed, a fair number of important jobs -- assistant secretaryships, general counsels and regulatory commissioners -- remain to be filled.

But as one black insider put it, the approximately 500 sub-Cabinet jobs "have all been spoken for at least 10 times." Without some clear signal from the president himself, it is unlikely that many of these jobs will be filled by blacks.

This is true two reasons. First, there is a relative dearth of black Republicans, let alone blacks who were in the Reagan camp prior to the election. Second, in the words of one black Reagan appointee, those under consideration for the top-level posts "come from states, and the state Reagan-Bush people have sign-off on these jobs. They've got some people they have to take care of."

It may be that the most distressed of the black Republicans are those who had hoped that the Reagan administration would go easier on the question of loyalty to Reagan in particular and instead would move to reward black Republicans as a means of enticing more blacks into the Republican camp.

Which would seem to make a lot of sense for a minority political party.