The letter from the Massachusetts Department of State Police arrived without warning or explanation, ordering Donald Landry to report to a National Guard armory and give a blood sample for DNA analysis.

Landry is a convicted murderer with priors for car theft, breaking and entering, and armed robbery -- ostensibly the sort of person whose DNA the police would like to have on file: Somebody is killed, lab techs run tests on the saliva stain on the cigarette butt, and bingo -- they match the crime-scene DNA to a career criminal.

Except Landry, 61, was paroled 21 years ago, and hasn't been in trouble since. He's married, has three young children, and lives quietly as an unemployed roofer about 20 minutes south of Boston. Not only did he not want to give a sample, but he had to pay $110 to have it done.

"I've been out of trouble for so long, and all of a sudden they come out of the woodwork and do this," Landry said.

Landry is caught up in a nationwide rush to make DNA analysis a leading forensic tool of 21st century law enforcement. Four years after the O.J. Simpson trial, DNA profiling is universally recognized as a technology that can free the innocent, condemn the guilty, identify a perpetrator with court-testifiable certainty and close cases that have languished unsolved for years.

But DNA's potential has pushed politicians to authorize sampling of ever larger numbers of Americans. First came sex offenders, then all violent criminals. Some states, such as Virginia, take samples from all convicted felons and some juvenile offenders. Louisiana has passed a law to sample anyone who is arrested for any crime. New York Mayor Rudolph Giuliani suggested the state sample infants at birth.

Official enthusiasm for DNA analysis has raised alarm bells among those worried about abuse of Fourth Amendment privacy rights: "Some people ask why the government should be allowed to do this," said Massachusetts public defender Benjamin Keehn, who represents Landry and six others who challenged the state's sampling law. "Others say, `Well, these people are just criminals.' " But good or bad, he added, DNA sampling "is a serious expansion of governmental power."

Although DNA evidence appears to have come of age, there is little law that covers it. Besides questioning the constitutionality of DNA testing, the ACLU and other advocates are also worried that many states fail to destroy samples after DNA analysis is complete.

"People who committed crimes should be prosecuted," Landry acknowledged. "But I also feel that if they're allowed to do this to me, does it stop with me? Can they take anybody's DNA and put it in a bank even if they didn't commit a crime? Where does it stop?"

DNA is potentially much more invasive than fingerprints, critics note. Besides establishing someone's identity, analysts can use DNA to determine whether a person is at risk for certain diseases. And someday, scientists may be able to identify those with a genetic disposition toward alcoholism, mental illness and, perhaps, even rape, murder and a host of other behaviors.

"DNA harbors our innermost secrets," said Barry Steinhardt, an associate director of the American Civil Liberties Union, "and those of our families."

All 50 states collect DNA samples from some convicted felons, and legislation is pending in Congress to gather samples from federal offenders in the District, in the armed forces and on Indian reservations.

Most states are using DNA analysis in casework, and 103 crime labs have tapped into the national DNA database that the FBI opened last October. With only 184,000 DNA samples on file, the Combined DNA Index System (CODIS) hardly rivals the 226 million fingerprint cards in the FBI's Criminal Justice Information Services Division, but the agency believes CODIS's time will come.

"Eventually it will include all states, and all felons," said CODIS program director Steve Niezgoda. "There are 1 million felony convictions each year in the United States."

DNA analysis has produced some spectacular results. Since October, CODIS has registered 600 "hits" on DNA samples. Virginia has used DNA to solve 60 cases in six years.

In a recent speech, Sen. Herb Kohl (D-Wis.), sponsor of the pending federal legislation, described how DNA analysis linked a suspect to four rapes in two Wisconsin cities, resulting in an 80-year prison term.

Attorney General Janet Reno asked the National Institute of Justice to convene a National Commission on DNA Analysis after she read about several cases in which DNA evidence had cleared prisoners. The Innocence Project at New York's Cardozo Law School used DNA evidence to help free eight people from jail.

Last year the Massachusetts public defender's office and the ACLU challenged the state's new statute ordering DNA samples from offenders convicted of any of 33 crimes ranging from murder to prostitution.

The seven plaintiffs included Landry, who was found guilty of first-degree murder in the 1964 shotgun killing of a man. Landry insisted the killing was an accident, and he was paroled in 1978.

The plaintiffs won their case at trial but lost on appeal in April. Keehn, the lead attorney, plans to ask the Supreme Court to hear the case, but he doesn't hold out much hope. The court has refused to hear two similar appeals -- one from Virginia.

"We use the same basic argument [as the other cases]: The fact that someone has been convicted of a crime in the past isn't enough to justify this kind of search and seizure," Keehn said. The courts, however, have agreed with plaintiffs that "once you have been convicted of a crime, you have a reduced expectation of privacy," he added.

But if the initial battle over constitutionality is lost, there are others to be fought: what to do with tissue or fluid samples after DNA analysis is completed; whether it is legal to require DNA testing for anyone arrested for any crime.

It may be too early to worry about arrestees. The FBI's Niezgoda says that although 43 states are using CODIS, only 14 are putting DNA profiles into the database. Many states are still doing preparatory work or lack the funds, lab facilities or trained personnel to analyze the samples they have collected.

Christopher H. Asplen, executive director of the Justice Institute's Commission on DNA Evidence, estimates that 500,000 samples taken during the last four years are awaiting analysis and that an additional 1 million to 1.5 million offenders qualify for testing that has not been done.

"All of these people should be in the database, but there's no money to test them," Asplen said. "Nowadays, a rapist gets convicted and the police take his blood, but they don't analyze it. On parole he commits another crime, and we get a great rape-scene sample, but we don't have a profile in the system."

And besides the known offenders, there also is "a boatload" of rape kits, bloody rags, cigarette butts, Styrofoam cups and bits of hair that have languished in police department evidence closets for years, Niezgoda said. New York City alone has thousands of rape kits awaiting analysis.

For these reasons, the FBI and the commission prefer to leave the question of arrestee testing until later: "States [are] saying, `We're going to grind to a screeching halt if this happens,' " Asplen said. "Once we get a system that's up to speed, we can start doing these other things."

Louisiana, the only state with a law mandating arrestee testing, has delayed implementation because it lacks funding and a proper facility.

Clearing the backlog is "just a matter of money," Niezgoda said, and there is $30 million in the Kohl bill earmarked for that purpose. Asplen believes that by using the money to hire outside contractors, CODIS could be up to date on offender samples in 18 months. Without the money, it could take six years.

Other difficulties would remain, however. Most of CODIS's samples were filed using an older, slower analytical method than the technology the FBI is promoting.

But the conversion will require a lot of re-analyzing, so, Niezgoda said, the FBI is encouraging states to hang on to their samples. "The cost of collecting a sample far exceeds the cost of analyzing it," he said.

Indeed, Asplen estimates that a private contractor can do a DNA analysis for considerably less than $50, well below half the $110 Massachusetts wanted from Landry to collect his sample.

CODIS requires sampling from 13 "loci" along the human genome, and Niezgoda emphasized that the loci are "junk DNA," useless for any purpose other than identification.

But according to the ACLU's Steinhardt, no law enforcement jurisdiction has ever gotten rid of its samples, and there is no law requiring them to do so. The ACLU, he added, is "urging" the destruction of samples "to remove the temptation to do other types of examination."

Who Gets Tested

All states require DNA samples from sex offenders. Most states require samples for offenses against children (40) and for murders (35). For other offenses, the requirements vary greatly from state to state.

Offenses for which states require DNA samples

* States in bold require DNA registry for any felony committed.

State Assault Robbery Kidnapping Burglary

* Ala. X X X X

Alaska X X X O

Ariz. O O O O

Ark. X X X O

Calif. X O O O

Colo. O O O O

Conn. O O X O

Del. O O O O

Fla. X X O O

Ga. O O O O

Hawaii O O O O

Idaho X X O O

Ill. O O O O

Ind. X X X X

Iowa X O X X

Kan. O O O O

Ky. O O O O

La. X O X O

Maine X X X X

Md. X X O O

Mass. X X X X

Mich. O O O O

Minn. O O O O

Miss. O O O O

Mo. X O X O

Mont. X X X O

Neb. O O O O

Nev. X O O X

N.H. O O O O

N.J. O O O O

* N.M. X X X X

N.Y. X O O O

N.C. X X X O

N.D. O O O O

Ohio O O X O

Okla. X O O O

Ore. O O O X

Pa. O O O O

R.I. O O O O

S.C. O O O O

S.D. O O O O

Tenn. O O O O

Tex. X O O X

Utah O O X O

Vt. X X X X

* Va. X X X X

Wash. X X X O

W.Va. X X X O

Wis. X X O O

* Wyo. X X X X

SOURCE: FBI

CAPTION: Paroled in 1978 after serving time for murder, Donald Landry -- with wife Mary Ann, son Charlie and their dog in Whitman, Mass. -- fears errors in DNA profiling.