Among many non-issues in the presidential campaign in France, defense spending surely ranks alongside the preservation of historical monuments, the declining purity of the French language and the merits of this year's Beaujolais.

West Germany, Britain and small northern European countries may plead that they cannot afford to meet their North Atlantic Treaty Organization commitments to raise military expenditures by an inflation-adjusted 3 percent annually. But France, facing similar economic problems, has encountered no political resistance to a budget that increases its defense spending by about 5 percent for 198l.

The parliamentary record in recent years makes no mention of defense bills getting bogged down in committee hearings. Rarely has an opposition legislator here questioned the price tag on a new missile or jet fighter. With less than five months before elections, no Communist or Socialist politician has yet proposed to President Valery Giscard d'Estaing that with unemployment reaching postwar record levels and inflation at 14 percent the military budget should be trimmed in favor of social expenditures.

with no sign of public opposition, France also has become the third biggest arms salesman after the United States and the Soviet Union, with a jump in weapons exports from $620 million in 1970 to more than $5 billion this year, to customers ranging from right-wing African dictatorships to radical Arab regimes.

There has been no fallout either from French military interventions abroad, whether successful, as in Zaire in 1978, or failures like Chad, where Libyan troops this month swept through the country after French forces pulled out of the civil war.

Most explanations for this lack of controversy accorded the defense issue in France dwell on the structure of the political system wrought by Charles de Gaulle more than 20 years ago. The strongly centralized government he created made defense and foreign policy virtually the exclusive prerogatives of the president.

"When you consider also that there is no sense of military threat in France the way one immediately feels it in West Germany, it is not surprising that there is a tendency among the French to let the president assume full responsibility for defense questions," said Thierry de Montbrial, director of the French Institute of International Relations, the only nongovernment think tank to concern itself with defense issues.

"With such a low level of public interest, the average legislator just does not feel it is worth his while to learn complicated military dossiers or make himself knowledgeable on defense," Montbrial said.

"The situation in this respect is a lot different from an ambitious American senator working with staff of researchers."

According to Jean-Pierre Cot, a Socialistt deputy often mentioned as one of his party's few defense experts, the leftist opposition has been loath to assume the role as critic of defense spending because it was identified for so long with utopian pacifism.

"It was only in the very recent past -- 1975 to 1978 -- that the Socialists and Communists gave up their antinuclear positions and accepted the idea of a force of military dissuasion," said Cot. "And while we have abandoned simplistic antimilitary attitudes, there has not been very much deep reflection on just what level of defense spending is desirable, or what kind of military programs should be pursued."

It was during this period of change in leftist attitudes that French defense spending began rising. Since 1975, the military budget has grown annually by about 3.5 percent to about $21 billion in 1980. The largest portion of these increases has gone into modernizing De Gaulle's famed force de frappe -- the nuclear deterrent aimed at assuring French military independence. Once debunked as an insignificant arsenal, French nuclear power has tripled in the last four years, reaching 75 megatons -- about one-fifteenth that of the U.S. Minuteman force but still enough to level most of the western Soviet Union if it penetrated Soviet defenses.

Plans call for replacement of the vulnerable 18 land-based missiles with longer range, mobile projectiles perhaps mounted on truck platforms to make them more elusive targets for enemy missiles. By 1985, the six nuclear submarines will be equipped with multiple independently targetable missile heads.

The 37 Mirage strategic bombers, the weakest part of the force de frappe because they require midair refueling, are to be modernized with air-to-ground missiles during next few years. The main thrust of conventional defense expenditures is to build a 10,000- to 15,000-member military force capable of quickly being dispatched to Third World trouble spots, particularly Africa.

Because this military buildup has been accomplished with little political friction, some foreign diplomats tend to laud the French defense establishment's handling of its public relations task. One Western defense analyst singled out the French development of a neutron warhead as a "masterful stroke in terms of preparing the pulic."

The weapon, first developed as a concept in the United States, ran into a storm of public criticism in Western Europe as "the ultimate capitalist weapon" because it would kill people without destroying property.

President Carter reversed a decision to deploy the weapon in Western Europe, where it had been hailed as a counterweight to the Warsaw Pact's overwhelming superiority in tanks, but earlier this year, Giscard announed with little fanfare that France had developed its own neutron weapon.

"the military and the president's office were careful to give press briefings on the pros and cons of the bomb for months before Giscard made his announcement," a diplomat recalled. "There were lots of little trial balloons leading to what amounted to a nondecision that the weapon had been tested but not deployed. The next step will probably be to deploy it, well before the decision is publicly announced."

Cot, the Socialist legislator, is less impressed by the government's public relations skill on military issues, and gives far more weight instead to the defense establishment's ability to plead secrecy against efforts by opposition deputies seeking information on weapons programs.

"The real debate over the military budget level in France takes place within the government bureaucracy, between ministries, and not at all within the parliament," he said.

"I suppose in this sense there is not much difference in the way military affairs are handled in France and in an Eastern Bloc country . . . it does not resemble a Western country, where the parliament has a final say."