IKE PETERS, an avid collector of artifacts from World War II, was once an enthusiastic user of online auctions. Every day, he logged on to Yahoo Auctions or eBay and trolled for uniforms, helmets, medals, flags, bayonets and books. Sometimes he would come across items that had belonged to Nazi soldiers, and he would snap them up, proud to fill a gap in his collection.

Those sources have all but dried up for Mr. Peters. In the past year, both Yahoo Auctions and eBay have taken steps to prohibit members from selling any items, except coins and stamps, with Nazi insignia. Officials for both companies say the rules were in response to complaints that auction services were making money from Nazi memorabilia and from reproductions of Nazi artifacts.

Last week, eBay expanded its ban to include not only items that were less than 50 years old — a rule the site instituted in 1999 — but all Nazi war pieces, regardless of age or authenticity. Yahoo announced a similar ban in January.

The bans make no distinction between legitimate collectors like Mr. Peters and Nazi sympathizers looking for props to promote their cause.

"So we're all being painted as neo- Nazis?" asked Mr. Peters, a 45-year- old restaurant owner in Westchester County. "Is there no such thing as an amateur historian?"

Mr. Peters and several other collectors said that the new rules were tightening the market for historical artifacts. Before the bans, collectors had been able to find items that might have been gathering dust in the attic of a noncollector, someone who had simply found a box of old medals and decided to put them up for bids.

"There were some rare and historic materials I would never have found elsewhere," said C. R. Davis, a former federal law enforcement agent and retired Air Force officer who lives in Bellaire, Tex. For example, he said, sons and daughters of World War II veterans were often good sources of Nazi items because soldiers had carried home objects like German belts or badges as reminders of battles they had won.

Mr. Peters, who uses an old Army jeep for deliveries, has been collecting World War II memorabilia since he was a teenager, when a neighbor gave him a German Army helmet. He has since built a collection that fills an entire room — the location of which he asked to keep private for fear of attracting thieves.

Flags, most of them with bold swastikas, are pinned to the walls. Uniforms worn by American, Italian, German and British soldiers are displayed on tailors' busts. Boxes of medals are stacked in front of overflowing bookcases.

Several times a year, Mr. Peters exhibits many of these items, but not the Nazi flags, at veterans' hospitals and at military memorabilia shows. His only hope, he said, is that the bans by eBay and Yahoo will not make people afraid to show interest in these items.

"To see a Nazi uniform and be able to say, `Oh, my God, this survived' — it's like reaching into history and having proof," Mr. Peters said. "It says, `This really happened.' "

To Mr. Peters, the auction bans attach an unfair stigma to artifacts of history. Out of embarrassment and shame, he said, sales are being pushed underground, where prices are higher and values inflated.

"It's like Prohibition," he said. "It's going to have the reverse effect."

Collectors have access to smaller, niche-oriented online auctions, like Manion's (www.manions.com), a Web site specializing in war memorabilia auctions. But they argue that those sites are known to few people outside the collecting world. Ron Knoch, a marketing director at Manion's, said he understood why World War II collectors would be upset to lose eBay's mass audience. "It has made communication so much harder," he said. "It's a real disadvantage for the collector market."

Kevin Pursglove, an eBay spokesman, said that officials at the auction company were aware of those arguments and had been discussing the impact of an outright ban for several months. But he said there were other factors to consider, like the problem of being an increasingly global company with members in countries that have outlawed the sale or display of items with swastikas and other Nazi insignia.

Yahoo confronted that conflict head-on in November, when a French judge ordered the company to block French users from viewing Nazi items on Yahoo's American site. The order, which Yahoo is fighting in Federal District Court in San Jose, Calif., raised questions involving international law and the problem governments face in trying to regulate the Internet.

Issues of international law aside, both auction sites have been under pressure from anti-defamation groups, like the Simon Wiesenthal Center, which argue that eBay and other mainstream sites should not be marketplaces for material that symbolizes hate.

"Companies like WalMart and 7- Eleven aren't going to stock this stuff," said Rabbi Abraham Cooper, associate dean of the Wiesenthal Center. "Now, in the same way, you won't find this on eBay. We think that is a very good thing."

Several eBay users have expressed similar feelings. In a recent online discussion, one member called the Nazi material "racist trash that glorifies and profits from genocide."

But Mr. Peters contends that although some sellers are primarily interested in making money, collectors trade these materials because they want to exhibit items like uniforms as complete sets.

"Every one of these artifacts is a piece of history," he said, "and without those pieces, part of the picture of World War II is missing."