Robert Wampler says his collection of 70 pistols, rifles and other guns has taken him 20 years to assemble and is worth almost $25,000. It includes 26 engraved weapons, some dating back to 1864.

So Wampler was infuriated when federal agents arrived at his home in Mechanicsville, Va., outside Richmond, shortly before 7 a.m. on Nov. 18, 1976, and seized the 70 guns. Four of the guns have never been returned, he said yesterday. "There is no way to explain the trauma or the humiliation that is involved in something of this nature," he said.

Wampler was among several gun collectors and dealers who appeared at a news conference at the Capitol to protest alleged abuses by the federal Bureau of Alcohol, Tobacco and Firearms. It was staged by Rep. John M. Ashbrook (R-Ohio), an outspoken critic of the bureau.

Ashbrook yesterday accused federal agents of engaging in "tyrannical, Gestapo-type action" against legitimate gun collectors and dealers. "We're going to have to do a better job of protecting the rights of citizens to own guns, including collectors," added Rep. J. Kenneth Robinson (R-Va.), who also appeared at the news conference.

G. R. Dickinson, director of the Bureau of Alcohol, Tobacco and Firearms, said later that he would look into the allegations voiced yesterday by Wampler and others. But he noted that investigations of previous complaints by critics of his agency have failed to turn up evidence of abuses by federal agents.

"Every case they bring up we look into," Dickerson said in a telephone interview. "I know of no case in which an ATF agent has ever been charged with a violation of civil liberties."

Wampler, a stocky, soft-spoken man in a three-piece gray suit, who works as a personnel manager for a pharmaceutical manufacturer in Richmond, voiced numerous complaints about the federal firearms bureau at yesterday's news conference.

Despite threats that he would be indicted, Wampler said, he has never been charged with any firearms crime. He complained that he has spent $2,000 to $3,000 in legal fees and other expenses because of the seizure of his guns.

Sixty-six pistols and rifles were returned to him by the federal agency on June 1, 1979 -- about 2 1/2 years after they were seized. Four others -- described by Wampler as an unusual 19th Century "knife" pistol, shaped like a pocket knife; a World War II German-made Mauser pistol, and two shotguns -- are still in federal custody.

"I would like to know why I can't have the four guns back," Wampler asserted.

Federal officials said yesterday they could comment publicly on only some of Wampler's statements. They said they were barred by federal privacy restrictions from responding to other complaints.

Officials said Wampler's guns were initially seized after an undercover investigation turned up evidence that he was allegedly dealing in firearms without a license. Wampler disputed this allegation yesterday, saying that he had been told by a federal agent in 1965 that he did not need a license and had, therefore, allowed his license to lapse.

Government officials said 66 guns were held until last year because an investigation was still under way. They said they were precluded by privacy restraints from stating why the other four weapons are still being held.

But Peter B. Mastin, assistant special agent in charge of the agency's Washington district office, said, "ATF followed all judicial and proper administrative proceedings in the retention of those firearms." CAPTION: Picture, ROBERT WAMPLER . . . collection worth $25,000