Flanked by armed marshals and wearing black, execution-style hoods, the informers are led into the well-guarded federal courtroom here to tell grand juries lurid stories of drugs, money and late-night flights from Central America.

These hooded witnesses, who say they fear for their lives if their identities become known, are covert agents in an undeclared war now being waged in the Southwest against what U.S. authorities say is a massive invasion of cocaine from south of the border.

Based on the anonymous testimony of these witnesses and that of more normally attired federal agents, the normally jury here has responded with a flood of indictments against purported big-time drug smugglers Grand juries in two other Texas cities and in Las Vegas and Seattle also have been pulled into the investigation,w hich has stretched from the steaming jungles of Colombia to the air-conditioned coolness fo casinos on the Last Vegas Strip.

The central figure of the Texas investigations has been professional gambler Jimmy Chagra, a younger brother of flamboyant El Paso attorney Lee Chagra, who was shot to robbery of more than $400,000. Last month, Jimmy Chagra, 34, was indicted in Midland, Tex., on five counts of smuggling massive amounts of cocaine and other drugs from Colombia into Texas, Colorado and Florida.

Even in high-rolling Las Vegas. Chagra is considered. in the parlance of the town, "a big player." At Caesars Palace, where he lived as a celebrated guest while his lavish Las Vegas home was being built, Chagra is believed to be one of the biggest gamblers in the world. Undisputed testimony at his bail bond hearing showed that Caesars advanced Chagra more thatn $8 million during a four-year period from 1975 to 1979.

According to the testimony of one federal Drug Enforcement Administration investigator, Chagra gambled-and lost-$1.1 million at Caesars in one three-day period early in February of this year.

These known losses are seen by federal investigators as a fraction of the financial cornucopia sustained by the South American cocaine trade. A federal agent at the bail hearing testified that Chagra's acknowledged high-stakes gambling is a cover for his real occupation of "illegally importing dangerous drugs and narcotics into the United States and distributing them.

Chagra is the No. 1 target in an industry allegedly so profitable that it is undiscouraged even by maximum sentences. In recent months law-enforcement agents have seized air-planes and boats loaded with sophisticated electronic gear and large quantities of narcotics.

Last Nov. 29, off Port Arthur, Tex., investigators boarded the trawler Agnes Pauline and confiscated 40,000 pounds of Colombian marijuana estimated at a street value of more than $20 million. Earlier this month three more boats, owned by a loosely knit organization known as the "Cowboy Mafia," were seized off the Texas coast.

In Arizona, authorities have attempted to link the Chagras with the so-called "Columbus Air Force" headed by convicted drug smuggler Marty Houltin, who calls himself the "Flying Ace of the Dope Air Force.

Houltin, a 55-year-old former military pilot, was quoted in a High Times magazine article as saying that he has 100 pilots at his disposal and that they make up to $150,000 a year.

"The profits are incredibly high-that's the mother's milk of this business," says San Antonio-based U.S. Attorney Jamie Boyd, who obtained the indictment against Chagra. "Because of this there has been a dramatic increase in the smuggling of controlled substances into the United States."

Federal authorities say that the financing for many large-scale drug importations comes from upper-middle-class businessmen and professional people who have extra money to invest. Such investments have long been open knowledge in El Paso, a drug-conscious town that is separated from the rest of the West by deserts and a mountain range but from Wexico only by a shallow river.

A month ago, an FBI agent in **el Paso, O. Leon Dobbs, broke an unwritten rule that this "respectable" underwriting of criminal investment go un-mentioned. Dobbs warned 70 members of the El Paso Downtown Kiwanis Club that businessmen who knew about illegal activities had six weeks to turn themselves in or face prosecution.

"There is an attitude problem among some rich persons in El Paso," Dobbs said in a subsequent interview. "Doctors, lawyers and businessmen invest money in crime. Then they pretend they don't know about the investment they've made in illegal drugs. And some get a 25 percent profit or more a week."

Local businessmen and the mayor complained about the speech and Dobbs was reportedly ordered by his superiors to stop giving aultimatums or newspaper interviews but there is a general belief in El Paso that his warning has made potential investors more wary.

Following the money trail of the major drug distributions in the United States has proved almost as difficult as tracking the investors. Boyd says that various investigators are trying to find out if large amounts of currency are taken to Las Vegas and "laundered" as investment or gambling income.

Las Vegas is a favorite rendezvous of big-time operators on the edge of the law, because of a lifestyle which appeals to them and because it is easy to change money in the casinos with-out attracting attention.

According to testimony in the bail heaing, Jimmy Chagra carried such large amounts of cash that he kept more than $900,000 in a footlacker in his Caesars Palace suite. At Caesars, Chagra was known as a lavish tipper who once gave $600,000 to a craps-dealing crew during a winning streak.

However, a Caesars Palace spokesman denied that Chagra or any other gambler had "laundered" money at the casino and said that it would be difficult to do so.

"there's absolutely no laundering going on here," says Richard Sheehan, general counsel for the casino and its parent company, Caesars World. "We have a number of carefully devised formal policies to prevent it that I'm convinced are being followed to the letter."

Sheehan contended, and testimony at the Chagra bail hearing confirmed, that Caesars had made its records available to prosecutors, including files on various aliases Chagra used there. The casino counsel said that Caesars, which is scheduled to open a New Jersey casino in May, also would make the material available to a defense attorney upon request.

"We cooperate with everyone," says Sheehan.

This sort of cooperative attitude does not prevail in Texas, where the prosecution of Chagra and his associates resembles a no-quater border war.

Lee Chagra, a popular attorney who was the target af an unsuccessful federal drug smuggling indictment in 1973, had before his death been preparing a lawsuit charging the DEA and a tough-talking depty U.S. District Court Judge John Wood made no secret of their belief that Lee Chagra's involvement in the drug business went beyong being a defense attorney.

After Chagra was murdered, El Paso police sealed his office and allowed agenst of DEA and the Internal Revenue Service to inspect various or his 4,000 legal files.

"The court finds there were criminal violations," El Paso District Judge Woodrow W. Bean II determined after conducting a court of inquiry. "The type of search conducted in this case distrubs the court and should distrub everyone. It would allow police to violate the files of a CPA, physician, lawyer, newspaper, clergy, banker, businessman or anyone else."

Though the county attorney declined to prosecute on these findings, the court of inquiry reinforced a belief in El Paso that authorities will do almost anything to get a Chargra, at 31 the youngest of the three brothers, believes this attitude is based upon the failure of the government indictment against Lee. He predicted after his brother's murder that Jimmy would be indicted and that material in the files would be used as leads by the prosection.

Jimmy Chagra has returned to Las Vegas where he is no longer a familiar figure at the crap tables. He is involved in a bigger gamble now, one that could cost him up to 45 years in prison.

Chagra is proud of his reputation as a gambler. That alone would be enough to earn the enmity of Boyd, the hard-nosed Texas prosecutor who wants Chagra behind bars.

"I've never met one who wasn't a liar and a cheat," Boyd says of gamblers. "Their whole aim is to get your money and way they can."

Now, the U.S. attorney believes, it is his turn to get Jimmy Chagra.