Nine years ago, 500,000 people took the semiannual entrance examinations for professional jobs with the federal government. Last month, when the government offered its first nationwide job test since 1981, only 85,000 applicants showed up.

The dramatic drop in the number of people seeking jobs on the government's management track provides the strongest evidence to date of the decline in the prestige and attractiveness of government service, according to academic and union officials.

For almost a decade, since the previous test was discarded as discriminatory against minorities, the government has been experiencing difficulty recruiting high-quality applicants for many federal jobs. But the evidence has been anecdotal and spotty because a nationwide examination was lacking.

"This is a disappointing figure that signals a very serious problem," said Paul Light, associate dean at the University of Minnesota's Hubert H. Humphrey Institute of Public Affairs. "This cannot be explained away as a timing problem or an advertising problem. The problem is that young people are no longer interested in government careers."

"The government is just not getting the people it used to," said Janice LaChance, political director of the American Federation of Government Employees. "It is pretty clear that a pool of half a million is better than a pool of 85,000."

Office of Personnel Management Director Constance Newman said she believes such conclusions are premature because the examination was given on relatively short notice after a nine-year layoff. Another exam will be given in the fall.

Ironically, the nine-year hiatus has produced important breakthroughs in employment testing that may make the government's tests far better than ever before.

The government has apparently improved its abilities to distinguish among large numbers of candidates without discriminating against minorities. Minorities are passing the current tests, according to preliminary figures, at a rate seven times higher than under the old Professional and Administrative Career Examination (PACE).

In 1981, the PACE was abandoned by the Carter administration in a consent decree after minorities charged that it discriminated against them. Only 5 percent of blacks and 13 percent of Hispanics passed the PACE, compared to 42 percent of whites.

Moreover, the fraction of blacks and Hispanics who actually got jobs was smaller because the government must rank applicants according to their scores on the test and hire one of the top three, giving preference to veterans. The percentage of blacks hired through PACE was 0.7.

In an agreement signed days before President Jimmy Carter left office, the government promised to replace the PACE with new tests that would "reduce or eliminate adverse impact to the greatest extent feasible."

This phrase was never defined because in nine years the government never completed the new tests. Specialized tests for specific occupations were developed, but there were no tests that could be given regularly nationwide for 100 job categories. The conventional wisdom was that the only way for the government to comply was to assure that the percentage of blacks and Hispanics who passed the test and got jobs was roughly the same as the percentage of whites.

Donald J. Devine, OPM administrator at the time, told reporters privately it was futile even to try to devise a test that was statistically valid, job related, and without adverse impact on blacks and minorities.

The government used a system of "informal quotas" in making hiring decisions during this period, Devine said recently in an interview.

But by 1987, a U.S. District Court judge overseeing the case had lost patience with OPM's failure to comply with the consent decree and demanded that tests be reintroduced for all 118 professional and administrative occupations covered by PACE.

The new tests, finally completed in April, were offered in hundreds of locations around the country last month at a cost of roughly $1.5 million, according to Leonard R. Klein, OPM's associate director for career entry and employee development. Of the 172,000 who signed up, roughly half took the test and about 60 percent passed.

"I think it is way too early to draw the conclusion that college students have lost interest in federal jobs," said Newman. "I already know we have a problem with pay and with image, but it is premature to say that this proves anything beyond that the tests were announced late."

"All in all it was a reasonable turnout," Klein said. "We went out {with our announcements of the test} in May, and a lot of schools have their graduations in May.

"Schools were used to the PACE," he said. "It was given twice a year, the flow was there. We stopped for a decade; now we have to crank the motor up again."

"It's going to take a three- or four-year effort to rebuild a network of people who know about the test," said Mark Abramson, president of the Council for Excellence in Government. "I'm not convinced there is a lack of interest in government careers. It will take time to get back in the college recruitment game."

"The PACE was a regular spring ritual and a lot more people took it than really planned to go into government," said Alan K. "Scotty" Campbell, a former OPM director. "I'm not ready to say that this is proof of a decline in interest in government jobs until they have another set of exams."

"I don't think the damage is irreparable," said Bernard Rosen, former executive director of the Civil Service Commission. "I think we need to promote the desirability of federal employment among college students."

The nine-year hiatus in nationwide testing has virtually dismantled the publicity apparatus the government relied on to inform people about the test. And in a tighter labor market, many of the smartest students are no longer willing to take a 3 1/2-hour test and wait to get a job only if they score among the top three applicants.

In addition, schools and other institutions are no longer willing to allow the government to use rooms without charge. For the first time this year, OPM had to pay for testing rooms in many places, Klein said.

Meanwhile, the federal job market is depressed because of defense cutbacks. Only 5,000 people are likely to be hired from the lists generated by the exams, according to Klein.

"If we have 50,000 or 60,000 quality recruits for probably less than 5,000 jobs, I think that is enough," he said. "The only question is, are we getting the bottom of the class or the top?"