President Reagan has abandoned his plan to name Robert J. Brown the first black U.S. ambassador to South Africa and will announce no new U.S. sanctions in his policy statement on South Africa Tuesday, administration officials said yesterday.

The proposed nomination of Brown, a North Carolina businessman who served in the Nixon White House, was dropped after a White House meeting late Friday as a result of information produced by a background investigation, according to a senior official. The official declined to give details of the information, but all indications were that it involved business dealings that could have been sharply questioned in the intensive congressional review expected before Brown's confirmation.

White House officials were under instructions from chief of staff Donald T. Regan not to comment on the Brown nomination yesterday, and various spokesmen refused to do so. But there was no doubt that the turnabout on Brown, whose nomination was expected to be the centerpiece of Reagan's statement, left the administration embarrassed and devoid of a major new element of South Africa policy to announce with public and political appeal.

As currently envisaged, the Reagan statement in the East Room Tuesday afternoon will emphasize U.S. opposition to South Africa's apartheid system, promise greater U.S. dialogue with South African black leaders and call for more extensive international efforts to encourage racial change in South Africa in coordination with Great Britain and other U.S. allies that have influence there.

Absent from the president's statement in its present form are any new U.S. economic sanctions or moves toward disinvestment, as are being demanded by members of Congress and endorsed in recent days by California Gov. George Deukmejian (R) and the University of California Board of Regents, among others.

"I am very much opposed to punitive sanctions" against South Africa, Reagan told reporters Friday. Secretary of State George P. Shultz, who is among the principal architects of South Africa policy, has called forced disinvestment a "cop-out" and vowed that the United States must remain engaged.

A major administration concern is to keep in step with British Prime Minister Margaret Thatcher, who along with Reagan has been a key opponent of economic sanctions. British Foreign Secretary Geoffrey Howe, who met with Reagan and Shultz on a coordination trip to Washington late last week, reportedly gave no indication to officials here that Thatcher has decided to abandon her no-sanctions stand.

The key decision points for Thatcher are a special British Commonwealth meeting in London next month, when she is expected to come under heavy pressure to change her position, and a late-September deadline for a report to the European Economic Community on the issue.

Last September, Reagan announced limited U.S. sanctions -- such as banning computer sales to South African security agencies and stopping importation of South African kruggerand gold coins -- to head off congressional passsage of stronger measures. His one-year executive order establishing those measures runs out Sept. 9. A successor executive order could be the vehicle for new moves if Congress does not force earlier and possibly stronger action.

A major consideration in U.S. policy-making is the potential effect on other southern African nations of economic sanctions aimed at the Pretoria regime. A senior State Department official said Pretoria has warned Washington that any economic damage it suffers from sanctions will be sharply felt by neighboring black-led nations.

The proposed nomination of a black ambassador to Pretoria was conceived and promoted by senior White House officials as symbolizing a major shift in U.S. attitudes and deflecting political pressures without adopting economic sanctions. Brown, 51, made it clear that he opposes sanctions and backs the main lines of administration policy.

Brown's name was brought up about 10 days ago by Regan in a White House meeting and pushed hard despite State Department reluctance to assign an inexperienced layman to a key diplomatic post during a crisis. A background investigation was authorized on an expedited basis by a group involving Regan, White House Counsel Peter J. Wallison and State Department and National Security Council officials. The aim, sources said, was to make it possible for Reagan to announce his choice of Brown on Tuesday.

The tentative selection of Brown quickly leaked to the press and was informally acknowledged at the White House early last week. At the same time, reports were circulating of questionable dealings involving Brown or his business partners with a reportedly corrupt Nigerian figure and in connection with a Small Business Administration loan and labor controversies in North Carolina.

Brown, who could not be reached for comment yesterday, has denied all allegations of wrongdoing.

There is no expectation that another choice for U.S. ambassador, to succeed Herman Nickel, can be selected in time for Reagan's statement Tuesday, officials said.