The Supreme Court’s historic decision on the Second Amendment could make millions of felons eligible to own guns.

Under current federal law, the vast majority of felons are prohibited from so much as touching a gun or ammunition, on pain of punishment of up to 10 years in prison.

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Some legal experts now say that the constitutionality of that law, known as the “felon in possession” law, was deeply undermined by the Supreme Court’s decision Thursday in District of Columbia v. Heller.

In that case, the court held that the Second Amendment gives individuals the right to keep a handgun at home for protection. The court struck down a handgun ban in Washington, D.C. Gun rights groups have begun challenging bans elsewhere.

But little attention has been paid to the effect that the court’s decision could have on regulations defining which groups of people can be excluded from gun ownership.

“The Court might decide there are some classes of felons that ought to be treated differently from other classes of felons,” a former solicitor general, Theodore Olson, said in an interview on Thursday about the prospect that the Supreme Court may eventually permit felons to own guns.

Crimes ranging from murder to writing a hot check can count as felonies. The felon-in-possession law applies to people convicted of state crimes as well as federal crimes.

At the end of 2001 there were 5.6 million adult felons living in this country who either had been to prison or were still behind bars, according to Justice Department figures. But the number of felons is actually much higher because many felons are sentenced to probation and never do any time.

The only felons who can lawfully retain a gun, according to exceptions written into the statute, are those convicted of anti-trust violations or crimes involving unfair trading practices.

In interviews, several legal experts say that lower court judges should interpret the Supreme Court’s decision in Heller to permit non-violent felons to own weapons.

“Why not? I can’t see why they shouldn’t have gun rights if they don’t have a record of violent crime,” a lawyer who financed the Heller case, Robert Levy, said. “If the nature of their crime has nothing to do with the commission of violence than it’s a pretty strange punishment that would deprive ex-felons of the ability to defend themselves.”

While courts are likely to recognize the government’s interest in denying guns to those who have committed violent crimes, judges may question why the government seeks to disarm non-violent offenders, they say.

“The label felon is so broad and so oppressive that maybe it makes a useful shorthand when we assume guns are bad,” a law professor at Ohio State who has written on this issue on his influential legal blog, Douglas Berman, said. “But essentially Heller says the Framers thought guns were good and that guns are good in part to protect a basic civil right of self- defense.”

Among gun rights lawyers there is little enthusiasm for trying to arm felons, a cause that is unlikely to attract much popular support.

“I don’t sense any great interest in overturning the ban on felons-in-possession,” a co-counsel to Mr. Levy who argued the Heller case before the Supreme Court, Alan Gura, said in an interview. “I don’t see that as the next battleground.”

Regardless, the issue will arise as defense lawyers challenge the Justice Department’s routine prosecution of felons who are caught with guns.

In such cases, Mr. Berman said, a judge may look with sympathy on “some guy who did blow at a party 20 years ago and pleaded guilty to the wrong thing and now wants to go hunting with his grandson.”

The Justice Department is expected to vigorously defend its felon-in-possession law. Prosecutors like the law because it makes for some of the easiest criminal cases to prove: All that’s needed is proof of a felony and proof of gun possession. It provides a simple and direct way to put dangerous criminals behind bars, they say.

Felon-in-possession cases are commonly prosecuted across the country, although exact statistics were not immediately available. On a slow day, one habit of lawmen is to visit a pawnshop and look through the paperwork to see if any felons have recently pawned a gun, a former sheriff in Arkansas, Pat Garrett, said in an interview.

Justice Scalia, in writing for the majority in the Heller case, sought to foreclose these very kinds of challenges. The opinion suggests that only “law-abiding, responsible citizens” enjoy Second Amendment rights.

“Nothing in our opinion should be taken to cast doubt on longstanding prohibitions on the possession of firearms by felons and the mentally ill,” Justice Scalia wrote.

Yet, in a dissent, Justice Stevens suggested that the majority wasn’t being true to its own logic.

“Even felons (and presumably irresponsible citizens as well)” can invoke the Bill of Rights, Justice Stevens wrote.

Federal law also prevents people convicted of misdemeanor domestic abuse from keeping guns. The Supreme Court will hear a case, United States v. Hayes, on that law next fall. While a rather technical point is at issue, the Supreme Court could use it to consider what gun rights criminals have.