President Carter is preparing to announce an administration goal of doubling federal procurement from minority businesses over the next two years, according to informed sources.

This is one of only a few firm decisions that have been made to date during a comprehensive review that is just beginning to crystallize, the sources say.

Most federal purchases from minorities - an estimated $423 million this year - are made through a beleaguered Small Business Administration program in which contracts are in essence awarded to SBA to be subcontracted to small businesses.

Beginning with the Nixon administration's "black capitalism" drive of the early 1970s, the program, known as 8(a), has been the major method for routing federal contracts to blacks and other minorities.

Although 8(a) has been heavily criticized following recent Senate hearings that uncovered some instances of abuse, the increased purchases that Carter will announce will be made largely through the 8(a) program, sources said.

Apart from doubling procurement from minority business and strengthening 8(a) rather then throwing it out, few final decisions have been made about the adminstration effort, sources said.

Much of the groundwork, they said, was done by a task force under the direction of White House domestic policy adviser Stuart Eizenstat. The task force sent Carter a memo, sources said, detailing six recommendations for improving the existing programs, which have had little success in channelling minorities into the mainstream of the economy.

One of the six steps, in addition to the two Carter reportedly has approved, is wider application of a successful National Aeronautics and Space Administration program that makes minority subcontracting a condition of prime contact awards and identifies the minority firms in advance.

The other steps: creating a task force on formation of capital for minority businesses, strengthening an interagency council that coordinates minority business efforts within the bureaucracy, and generally supporting the two major agencies involved - SBA and the Commerce Department's Office of Minority Business Enterprise.

The sources stressed, however, that these are only suggestions, and have neither been set in final form nor approved by the President. "This is still a thrashing-out process," said one.

Extensive debate is expected over the last proposal - preserving SBA and OMBE as separate agencies.

Although the two perform different functions - SBA making contracts available, OMBE providing technical and management assistance - congressional sources contend that administrative problems could be eased and money saved by consolidating OMBE's functions under SBA.

"Contracts are an element, but they're not the whole story," said one. "If a guy needs marketing developement and administrative help, all the contracts in the world are not going to make him a success by themselves."

Details of Carter's program have been one of the better-kept secrets in Washington. The first indication something was afoot came two weeks ago, when SBA called the House Small Business Committee to relay a White House request that Administrator A. Vernon Weaver not be asked to testify as scheduled last Thursday on two minority business bills sponsored by Rep. Parren J. Mitchell (D-Md.).

SBA told the committee Carter planned a major announcement on minority business when Congress returns from its August recess, and did not want to risk new controversy in what was expected to be a hostile session between Weaver and the committee, sources said.