THE RAIN pours down at Dusseldorf airport. Former President of Portugal General Antonio Ribeiro de Spinola emerges from his plane and is quietly ushered into a waiting car. He is met by an adviser to the President of West Germany's right-wing party; when the President arrives, the two leaders will make clandestine preparations for the coup that will return General Spinola and his conservatives to power.

The General, his aides and bodyguards are taken inconspicuously to a fashionable restaurant where they will await the President. The General dines with gusto on wine and choice venison, chats casually about the extermination of Portuguese Communists and arranges for the President's delivery of money and arms to his insurrectionist forces. Twice in 1975 the General's attempts to set up a right-wing dictatorship have aborted--but the President's adviser assures him that this time, with his leader's assistance, things will be different.

Only it is not the President's adviser at all, but an imposter--West Germany's "undesirable journalist," an avowed socialist sympathizer, Gunter Wallraff. Spinola is the victim of an elaborate hoax, perpetrated over the course of many months, during which Wallraff. Spinola is the victim of an elaborate hoax, perpetrated over the course of many months, during which Wallraff has carefully recorded and photographed evidence of the General's subversive activities. And now, ignorant of his undoing, Spinola himself is about to deliver his own coup degrace, revealing the most incriminating information of all.

Gunter Wallraff's brand of muckraking goes one step beyond that of America's most celebrated jounalists, Woodward and Bernstein. Rather than inducing government employees to lead to the press, Wallraff becomes an employee himself, and then writes about his experiences, exposing the graft, deception and mistreatment he encounters along the way. His technique requires few accessories--false identification, perhaps, a varied wardrobe, change of moustache and glasses--for the most part, though, his own resourcefulness time and again enables him to escape from tight situations.

At twenty to four the President still had not arrived. General Spinola had finished his meal, and was anxious to meet the President. Wallraff could only stall for time: he had only learned of Spinola's visit the day before, and had not yet succeeded in finding a 'President' to greet him. The previous night he had approached several friends--a lawyer, a doctor, a publisher, a member of the Bundestag, a vicar and several professional actors--but none would agree to play the role. Now, despite frequent and frantic telephone calls, Wallraff could not find a suitable President. At four O'clock, he informed Spinola that his President would arrive when it got dark, for security reasons--and continued to call, and hope.

Wallraff's specialty, however, is not unearthing scandals of Watergate magnitude, but his exposes on the exploitation of common laborers, for which he has become a working-class hero and crusader for socialism. To further this cause, Wallraff infiltrates not only the government, but also industry, political and religious organizations. In his most celebrated case, he exposed fraudulent articles printed in the establishment newspaper Bild, an arm of the powerful Springer press.

THE UNDESIRABLE JOURNALIST, a sampling of Wallraff's work over the last decade, contains ten such exposes all told in a narrative, first-person format. This collection features his masquerades as a porter, a night watchman in a cigar factory, the representative of a ficititious Jewish organization, an assembly-line worker, a right-wing informer pretending to be a socialist party member, and an adviser to the President of a West German political party. At 38, Walraff has been a journalist and self-made undercover agent for 14 years, emerging for a press conference or to write a newspaper article, remaining public just long enough to make sure that an official investigation will get underway, then disappearing again to assume another disguise and another role. If there is a limit to his ability, it is that he is too well-known; his books have sold 1.5 million copies in West Germany alone, and another 2 million in translations throughout Europe.

In a final attempt to obtain a President, Wallraff tries to persuade an old friend to participate in the charade. Acting the part of a President, Wallraff contends, is easier than it seems; "What does a President need to do but look important and say "yes" and "no" in the right places?" The friend is convinced; Walraff tells him to wear a tie and buy an attache-case to make himself look important. The friend sets to his task, and Walraff returns to inform the impatient General that the President is on his way.

The Ministry deceives, the courts deceive, the factory-owners deceive, even the press deceives. Why should not Walraff deceive, if his final product is the truth?

I decided to conspire in order to take a look over the wall of camouflage, denials and lies. The method I adopted was only slightly illegal by comparison with the illegal deceptions and manouevres which I unmasked.

It is five-thirty when the 'President' finally arrives, to Spinola's great relief. The President is terse; he cannot stay long, as an important meeting will take place that evening. But the General understands; he is familiar with the busy schedule of political leaders and is most grateful simply to have the President's acquaintance. It is a manic scene, with the 'President' nodding "Yes, your Excellency," the General unctuously urging their cooperation, and Wallraff nimbly interjecting answers to every question directed at his President.

The President checks his watch his and announces he must depart. Arrangements are made for a future meeting in Geneva, which Wallraff does not intend to keep. Soon he will emerge again into the public eye armed with enough evidence to force Spinola's expulsion from Switzerland, an investigation of the right-wing politician Franz-Josef Strauss, who had been preparing to sneak Spinola into Germany, and the failure of General Spinola's attempt to take over Portugal.

"Deceive so as not to be deceived." The American public seems to have rejected this argument, as was indicated in 1978 when The Chicago Sun-Times lost its bid for a Pulitzer prize because of "deceptive" reporting techniques. Two Sun-Times reporters had secretly bought a Chicago bar and then chronicled the bribes they paid to city officials in order to keep it open. Their story created a sensation in Chicago, where it led to a widespread investigation of municipal corruption. But it angered Washington Post Editor Ben Bradlee'43, of the Pulitzer jurors, who objected to the false pretenses used to obtain the evidence.

BUT IS WALLRAFF'S TECHINIQUE to be dismissed so lightly as Bradlee suggests? One advantage of Wallraff's method has emerged with the current controversy over Woodward and Armstrong's book The Brethren, where to prevent the betrayal of confidential sources, their evidence is unverified and must be taken on faith. Because Wallraff's sources act involuntarily, there is no need to protect them, and he can thus offer full disclosure of sources and documentation of his evidence.

Nevertheless, there remains a defect, particular to Wallraff's method, that mars his objectivity. Teleological journalism--reporting with a singular goal, like the doctrinaire Marxism Wallraff's professes--blinds the investigator to other, equally important truths. This prejudice makes The Undesriable Journalist an uneven collection. Some of the narratives read like adventure novels; others, fraught with details of worker mistreatment in factories, sound like chapters taken from The Condition of the Working Class in England. No matter how scientifically he records his results with microphones, magnetic tapes and hidden cameras if Wallraff seeks only part of the truth, that is all he will ever uncover. For a man who deceives to avoid being deceived, Wallraff commits the gravest error of all: self-deception.