With President Carter's approval, the Civil Serice Commission once again will require U.S. job seekers to answer questions about sex, race and ethnic background in their job applications, The Washington Post has learned.

The federal government had dropped all race and sex identification from job applications during the 1960s after civil rights groups complained the information was used to discriminate against minorities. Now, however, with the approval of the same civil rights groups, the government wants to obtain the information again to help in the recruiting of more women and minorities.

In recent years, the government has hired and kept track of its affirmative action progress by having supervisors look at employees, often guessing as to their race and ethnic backgrounds. Civil rights groups now argue that the climate has changed and that lack of reliable informaiton about job applicant's race and background hampers officials' efforts to hire minorities and to monitor their careers.

Federal officials said yesterday they do not know precisely when the new information will be required of job candidates, but they expect the questions to be on application for various professional, clerical and technical jobs early in 1978.

The program, one of many affirmative action steps being planned by the Carter administration, eventually will be expanded to cover most of the government's 2.6 million jobs and to contractors doing business with it.

The new program is expected to be formally announced by the Civil Service Commission in 10 days. CSC chairman Alan K. Campbell yesterday confirmed the return to asking the questions on applications and said the information "will be used as research for perfecting a means to collect such data in all federal examinations as soon as a system can be developed."

In addition to giving the government information on the numbers of minority group employees hired. Campbell said it will also help "to insure that selection procedures including written tests do not discriminate."

If, for example, it is determined that minority group members consistently fail certain tests, hiring data will reflect that "and those tests will be re-examined" to see if they have a cultural bias, said one official.

Although the government already has information on the race, sex and ethnic background of its workers, the material is computerized and kept separart from an individual employee's employment records. It is valuable, officials say, only in determining ethnic, racial, or sexual makeup of agencies after people have been hired. The current identification of workers is done by the so-called "eyeball" methods, meaning that supervisors look at a worker and designate his race or ethnic background.

At one time U.S. job application forms required candidates to submit a photograph of themselves. Applicants also were forced to check a box designating their race.

After the racial designations were dropped some agencies continued to use in-house codes (often a number or letter) to differentiate between blacks and whites. That, too was outlawed.

In recent years the government has tried self-idenfication. That left it up to the employee to designate his or her race and ethnic background. That system fell apart when thousands of State Department workers listed themselves as American Indians in an apparent protest against any form of racial designation. Currently the supervisor-designation is what the government uses to get its computer data on race, sex and ethnic back ground.

CSC officials say that eventually they hope to have all government workers list their race, sex and ethnic identification. This would make it easier, they say, to follow the progress of minorities in employment.