Last year's Proposition 13 "bomb-shell" has turned into a profusion of less-spectacular - but still potentially explosive - political fireworks.

When Californians approved the property tax-cutting initiative in June 1978, predictions were that the shock waves would shake the nation, first rippling through the states and eventually rocking even the free-spending federal government.

Now, 12 months later to the week, no such Sodom-and-Gomorrah scenario has come to pass. Only six states have since enacted genuine tax- or spending-limitation measures, and most of these are far less stringent than Proposition 13. And the impact in Washington has been mostly symbolic.

Alan Greenspan, President Ford's economic adviser, complains that for all the political rhetoric in the wake of the California vote, the measure has had "surprisingly little" impact across the nation. "I would scarcely describe the country as having been swept by Proposition 13 fever," Greenspan says.

Admittedly, there's been some movement toward tax-reduction and budget-cutting over the past 12 months.

The question is whether these modest moves are the result of the Proposition 13 vote a year ago or simply reflect a continuation of the belt-tightening mood and voter frustration over government that began well before the California referendum burst into the headlines.

Moreover, experts says the real ignition point could come next year, when the new Proposition 13 movement collides head-on with an expected economic slowdown. Analysts warn that unless state governments loosen their restrictions, the movement may backfire on its sponsors.

"The states are going to be in financial straits next year as it is," notes Rudolph G. Penner, a fiscal specialist at the conservative American Enterprise Institute."Whether the Proposition 13 movement will survived a recession remains to be seen."

In pure statistics, the Proposition 13 movement has scored some impressive victories:

Proponents have succeeded in pushing through tax- and spending-limitation amendments in six states since Proposition 13 was approved, and similar measures are scheduled for consideration in 10 more states later this year and next. However, only two - in Nevada and in Idaho - were as stringent as Proposition 13.

A nationwide campaign to pass a constitutional amendment to limit federal spending won endorsement in 30 states - only four short of the number required to call a constitutional convention. (Any further action will have to wait until 1980. No more votes are slated in state legislatures this year.)

States and localities appear to have checked their spending somewhat over the past 12 moths. Commerce Department figures show state and local purchases have remained flat after adjustment for inflation during the past several quarters after rising sharply in the early part of 1978.

At the federal level, the impact has been marginal. President Carter's fiscal 1980 budget proposal probably was no tighter than it otherwise would have been, and Congress has not trimmed the White House spending plan by much.

But the threat of a constitutional convention has prodded federal law-makers into several procedural changes - including providing in the new congressional budget resolution for a detailed plan for balancing the budget by fiscal 1981.

Grover Norquist, director of the National Taxpayers Union's Tax Action Committee, says that the Proposition 13 controversy "sensitized" members of Congress into thinking more about the demands of conservative taxpayers.

The Brookings Institution's Robert W. Hartman agrees: "Proposition 13 made it a lot easier for many congressmen to vote for budget cuts. You didn't have to be quite a brave to take a conservative position on a spending bill after Proposition 13 as you did before."

Still, the heralded nationwide bang has been somewhat more muted than many observers predicted:

While 30 states have endorsed the idea of a federal budget-balancing amendment, Congress appears to have been at least partly successful in dampening enthusiasm for a cutback in federal outlays by pointing out repeatedly that the biggest cuts initially would be in grants to states.

For all the flurry over state tax- and spending-limitation measures, few of the proposals enacted so far have been very restrictive. In some states, the new limits are so liberal they won't have any practical impact unless the economy falls into a serious recession.

To some, Proposition 13 may have had a perverse impact: with widespread pressure to balance the federal budget, Congress may not be able to cut federal imcome taxes next year, as it ordinarily would in an election year.

In many ways, the assessment of Proposition 13's impact depends on what you think might have happened if the California movement had not been successful. The National Taxpayers Union's Norquist contends that as recently as 10 years ago, states might have spent the extra revenues brought in by inflation. Last year and this year, he notes, they cut taxes instead.

Still, as both liberal and conservative analysts point out, the nation already was moving toward some governmental belt-tightening well before Proposition 13 captured the public's eye, and probably would have continued if the California measure hadn't passed.

As Penner argues, the real measure of the movement may not come until 1980.