The Reagan administration is establishing another front in its war on illegal drugs by expanding its much-publicized campaign to intercept smugglers in South Florida to six cities in an effort to cover all borders of the United States.

The National Narcotics Border Interdiction System will draw on Central Intelligence Agency informers, surveillance by Army and Navy helicopters and domestic crime-fighting agencies in hopes of intercepting more drug traffickers as they cross the borders, administration officials said.

The system essentially would expand on the effort in south Florida to combine military and law enforcement agencies in a stepped-up effort to intercept smugglers as they enter the Miami area. Enforcement efforts there have driven the traffic to other points along the border, administration officials said.

Vice President Bush, who headed the Florida task force, also will direct the national system, to be targeted at all foreign drug traffic--not just Latin American sources, focus of much recent administration attention. Bush is to unveil the program and name the six cities in a speech on Friday.

At the same time, the General Accounting Office yesterday released a report criticizing the federal government's anti-smuggling efforts as fragmented, and recommending that President Reagan create a central authority--a sort of "czar"--to coordinate the many agencies and task forces at work on the problem.

Reagan last year vetoed a major crime bill creating such a position at the Cabinet level, contending that it would add unnecessary bureaucracy and confusion. The move angered both conservatives and liberals, and a similar measure has been introduced this year.

Although the federal government has tripled its spending on efforts to curb drug smuggling since 1977, the GAO said, law enforcement agencies seize only 16 percent of the marijuana and less than 10 percent of the heroin, cocaine and dangerous drugs entering the country. The GAO said 95 percent of the smugglers arrested are low-level violators who spend less than a year in jail.

The Reagan administration has attempted to resolve the coordination problems between the agencies that police drug traffic--the Drug Enforcement Administration, the U.S. Customs Service and the U.S. Coast Guard--by creating 12 regional task forces under Attorney General William French Smith to investigate and prosecute smuggling and by setting up the South Florida program.

But the GAO said serious breakdowns still occur throughout the drug enforcement program.

The DEA performs follow-up investigations of arrests by the Coast Guard or the Customs Service, but only if the cases are to be prosecuted by a U.S. attorney. This covers only 40 percent of the arrests, the GAO said, meaning that information potentially valuable to future probes is being lost. "It is obvious that there is still no clear understanding between DEA and customs regarding their respective roles in drug enforcement," the report said.

In South Florida, the GAO said, federal statistics show a drop in the crime rate since the task force was organized, along with steep increases in drug seizures. Administration officials said $4.5 billion of cocaine and marijuana has been confiscated there.

But only about 5 percent of those arrested are major drug violators and the effort has caused smugglers to move elsewhere, the GAO said. In addition, the report said, the availability of illegal drugs nationwide has increased.

The Justice Department took exception to the GAO report, saying its 12 task forces can solve the coordination problems.

Administration officials said the border program will coordinate teams of federal agents already assigned to anti-smuggling efforts. Radar-equipped military helicopters, used for the first time in South Florida to help intercept smugglers in ships and low-flying aircraft, will be used on a larger scale along with CIA intelligence on smugglers, the officials said.

The GAO said the use of military helicopters in South Florida helped detect smugglers, but also was marred by coordination problems.