A fictional President's dispatch of troops to halt imaginary Communist aggression in the 1980s has generated enough furor here to underscore this haunting question: Can a post-Vietnam U.S. government ever again pose a credible threat to intervene militarily anywhere in the world?

That very question is the ideological underpinning of "Against All Enemies," a Washington novel by former LBJ speechwriters Ervin S. Duggan and Ben. J. Wattenberg. Their story has an American President, some 10 years after Lyndon Johnson, intervening in the right war at the right time in the right way (with limited forces). Yet he provokes such opposition that he is nearly driven from office.

Seldom has there been so vivid a cause of life imitating art. Reviewers of the book for the most inflential newspapers, including a former campaign speechwriter for Jimmy Carter, took precisely the same stand as the fictional President's enemies. While generally praising the novel, these critics recoiled at the notion of U.S. troops intervening anywhere under any conditions.

A similar mindset is found within the Carter administration's national-security bureaucracy, thereby moving this debate out of the literary salon. Suspicions have been raised about how the American superpower, deprived of the right to intervene, can confront the Russian superpower unshackled by self-limitations. Among the suspicious is novelist Wattenberg, who in the real world is mobilizing Democratic dissent to Carter policies.

In "Against All Enemies," liberal Democratic President Carl Rattigan faces an invasion of democratic Bolivia by Communist Chile. Impeded by campaign promises and his own doubts, Rattigan nevertheless intervenes - though with restraint not reminiscent of Vietnam. Restrained or not, the intervention triggers reflexive horror and a challenge in the New Hampshire primary by his own Vice President.

To conclude a fast-paced story, Duggan and Wattenberg put this New Hampshire victory speech in President Rattigan's mouth: "From now on, this President may be a little more reluctant to risk making hard, unpopular decisions. And future Presidents may be even more reluctant. The lesson . . . is that we're in deep trouble . . . If the world's strongest nation isn't willing to defend its values - with steel, if necessary - you can kiss those values goodbye."

This stemwinder follows 450 pages of reluctance and caution by President Rattigan, scarcely the happy cold warrior. Yet, the republication notice of the Kirkus Service called the novel "a dubious manifesto for interventionism," setting the tone for politicized reviews.

John Leonard, The New York Times daily book reviewer, writes that Duggan and Wattenberg "rattle a few sabers." In The Times Sunday Book Review, novelist adn sometime Carter speechwriter Patrick Anderson writes: "The message seems to be 'my President right or wrong," and after Vietnam and Watergate, that is a rather difficult message to accept."

The complaint is most explicit by journalist-novelist Aaron Latham, reviewer for The Washington Post: "I liked this political novel as a novel but disliked it as politics. If we must spread American steel around the world, I believe we should do it in the form of Coke cans." By complaining that Duggan and Wattenber "make foreign intervention seem defensible." Latham implies intervention is never permissible under any conditions.

That not only confirms the point of "Against All Enemies," it also echoes a disturbing view voiced privately by many Carter administration officials. Having left government service in opposition to Vietnam, they now "in Presidential Review Memorandum 10) discuss the option of not defending South Korea in case of enemy attack.

Carter provides no help. His book of campaign commitments ("Promises, Promises") contains this pledge: "Never again becoming militarily involved in the internal affairs of another nation, unless there is a direct and obvious threat to the United States or its peoples." Under that formula, President Rattigan could hardly have sent troops to Bolivia.

This disturbs such Democrats as Duggan and Wattenberg, who last week told the Women's Democratic Club here of their apprehension about the post-Vietnam United States functioning as a great power. Life and art intersect. Novelist Wattenberg, an occasional political operative, has resurrected the centrist Colaition for a Democratic Majority (CDM) mainly out of concern over the Carter foreign policy.

But the fictional Carl Rattigan, like the real Jimmy Carter, campaigned with post-Vietnam promises of nonintervention. If President Carter faces a Democratic ally in peril, might he imitate the novel and risk alienating his supporters, staff and even Vice President? Perhaps, but the critics of "Against All Enemies" suggest the political firestorm would be no less intense in real life than in fiction.