President Reagan announced the promotion of his highest-ranking black aide yesterday and the appointment of another black to the presidential staff to handle trade policy as part of a wider effort to improve the White House's relations with black Americans.

In announcing the personnel actions, deputy press secretary Larry Speakes said the administration is also contemplating other appointments and methods "to strengthen the administration's outreach efforts among minorities and the disadvantaged."

The elevation of Melvin L. Bradley, 44, from senior consultant to special assistant to the president was designed to "place a key black White House staff member in the mainstream of administration policy development" and to give him responsibility for continuously monitoring the impact of all administration policies "on minorities and the disadvantaged," Speakes said.

Yesterday's appointment of Wendell Wilkie Gunn, a conservative black Republican who is currently assistant treasurer for PepsiCo Inc., to be a special assistant to the president handling commerce and trade issues will bring the number of black presidential aides to six.

Reagan won office with less than 15 percent of the black vote. Black opposition to the administration's policies on civil rights, spending cuts for social programs and jobs has intensified in recent months. This has clearly been a source of concern in the White House.

"We've never had a large number of blacks voting for Reagan , but if this administration becomes a symbol of racism, then we will have a large turnout of blacks against us and liberal and moderate whites coming with them . . . , " Edward Rollins, assistant to the president for political affairs, told reporters last week. "I'm as much concerned about that problem as anything we face this year."

Black aides have also taken their concerns to Vice President Bush and senior White House advisers, asking that the White House respond in an effective way to the problem of high rates of unemployment among blacks and that the White House make an explicit commitment to defend their civil rights.

Left out of the decision making on policies affecting minorities and controversial black appointments but often finding themselves taking the heat for them from fellow blacks outside the administration, the aides established months ago an informal information-exchange network that one dubbed "The Soul Patrol."

"Patrol" members meet occasionally to discuss problems, then arrange for a member to use personal contacts with senior White House aides to lobby for policy changes.

Bradley, for example, lobbied counselor Edwin Meese III, with whom he has been associated since Bradley served as community affairs assistant on Reagan's California gubernatorial staff.

Steven Rhodes, White House liaison with mayors, lobbied deputy chief of staff Michael K. Deaver, whom he knew in California when Deaver ran a public relations firm that did work for Rhodes' employer, Reagan adviser Justin Dart.

Rhodes and Bradley addressed a Cabinet meeting late last year to urge unsuccessfully that the administration support the House-passed version of the bill extending the Voting Rights Act. Some black aides met with Reagan in January to explain the outcry that followed the decision to lift the ban on tax exemptions to segregated schools.

The Reagan administration came into office determined not to follow traditional procedures employed by previous administrations of both parties for establishing a link to black Americans.

After one strained meeting with black leaders of major civil rights organizations before the Inauguration, the administration has repeatedly resisted requests for Reagan to meet again with them, although individual leaders have been brought in for occasional sessions.

Senior advisers came into the White House with the feeling that the position of White House liaison with blacks, which had been standard in virtually every White House since President Eisenhower, was patronizing to blacks and to the person assigned to the job.

Shortly after the election, Meese, speaking to black conservatives in California, said that while Reagan intended to appoint blacks to high-level positions, "they're not going to be the ambassadors to the black people. They're going to be there because they have a substantive role to fulfill. You're not going to have one person that all blacks have to funnel through. I think that is demeaning."

But, after more than a year in office and as relations with blacks and some whites deteriorate, that is what the White House has now assigned Bradley to do.

Spokesmen said the new position is to give Bradley access to any Cabinet council meeting where he felt his voice should be heard. The promotion, however, does not give him enough status to be one of the regulars at Reagan's daily briefings.