One day last June, Juliet Cave got fired. "I don't know exactly why," she says. "I thought I was meeting reasonable goals. They told me I wasn't meeting a standard, but nobody knew what the standard was. It was probably just personal."

People get fired all the time, of course, and they're never very happy about it. But Juliet Cave's case is special.

First, she is a federal civil servant -- a GS 10 claims representative in a Social Security Office in Kansas City, Mo. She is 44 years old and has been with the government 19 years. Civil servants hardly ever get fired.

Second, she isn't fired any more.

Cave's boss thought that President Carter's much-praised Civil Service Reform Act of 1978 meant that she could be fired. The American Federation of Government Employes, a 300,000-member civil servants' union, thought otherwise. The AFGE won.

When it passed, the Civil Service Reform Act was greeted as the fulfillment of the central promise of Carter's presidential campaign: that he would make the federal bureaucracy more efficient and responsive.

But it's still very much up in the air what the act will really mean. That will depend on the outcome of a series of battles between the new Office of Personnel Management and the government employe unions.

Cave was a small part of the most important of those battles a lengthy and complicated dispute known as the Wells case, the crucial part of which will be ruled on this month.

For the most part, the Civil Service Reform Act was not very earth-shaking, even with the publicity to the contrary.

It replaced the Civil Service Commission with a new series of organizations -- the Office of Personnel Management, the Merit Systems Protection Board and the Federal Labor Relations Authority.

It replaced civil service grades 16, 17 and 18 with a Senior Executive Service that almost all the old supergrades have joined. In return for less job security, more than half of them are eligible to earn substantially more than the long-frozen top civil service salary of $50,112. It also provides for managers in grades 13, 14, and 15 to get pay raises based on merit, rather than on length of service.

For everybody below grade 13, the act could have a more important effect: it is supposed to establish the rating of those employes according to how well they perform the "critical elements" of their jobs. If they're not performing, the law is supposed to make it possible to fire or demote them.

It is over that provision that all-out war has broken out between the unions and the Office of Personnel Management.

The unions say that the OPM, as Rep. Patricia Schroeder (D-Colo.) put it, "seems labor relations." They now have more than 3,000 unfair labor practice charges pending against various government agencies, about double the usual caseload.

The OPM also is taking a belligerent line. Anthony Ingrassia, the OPM's assisant director for labor-management relations, said in a recent speech, "I find this atmosphere of dynamic tension good."

It's an unusual labor-management war because the federal employe unions, by law, can't strike and can't bargain over pay and benefits. That means they concentrate their efforts on behalf of their members on working conditions and especially "adverse actions" -- firings and demotions. Just about every time a civil servant is fired, the union files an appeal.

When the new law was passed, the unions and the OPM began circling each other warily, like wrestlers at the start of a match, waiting for the other to throw a hold.

The first move came last March, when an official of the Social Security Administration sent out a memo instructing Social Security supervisors to "develop interim critical elements on an as-needed basis to implement the unacceptable performance provision of the law." In other words, he gave the green light to firings.

In the following months, 41 Social Security employes around the country, most of them GS 10 claims representatives, were fired or demoted. One of them was Thomas Wells, who worked in the Sunbury, Pa., Social Security office.

The unions argued that "interim critical elements were illegal and immediately got the firings held up. Then the Wells case came before the new Merit Systems Protection Board, which in December handed down a decision agreeing with the union.

Because of the Wells decision, government managers have to come up with permanent performance standards before taking advantage of the new law. These are supposed to be in place by next October, but whether they actually will be depends on the outcome of yet another labor-management dispute growing out of the Wells case.

The unions want the right to negotiate all the new performance standards with management, saying this is only fair. The OPM says the negotiations would be so detailed and time-consuming as to make the new law on performance standards virtually meaningless. The issue is now awaiting a decision -- expected in about two weeks -- by the Federal Labor Relations Authority.

"If the unions win," says Ingrassia, "in effect, every management decision would be put into binding arbitration. That often takes a year. To get the performance standards done by October 1981 would be an insurmountable task. How well you can implement the performance standards is at the heart, the guts, of the Civil Service Reform Act."

The unions disagree violently with just about everything Ingrassia says, but they'd agree with that last sentiment. The performance standards are the heart and guts of the new law for them, too. That's the point about the Civil Service Reform Act: like so many important laws, what it really does will be worked out long after the signing ceremony in the White House, when the world is no longer watching.