WASHINGTON - Mail delivery in Sen. Patrick J. Leahy's office goes like this: Aides to the Vermont Democrat open the windows, slip on rubber gloves, sift through letters and then, in the most disquieting part of the daily ritual, start worrying about feeling sick.

It is not anthrax they fear, but its antidote. In recent weeks, some congressional aides have complained that mail on Capitol Hill, all of which is being irradiated to kill anthrax and other deadly agents, is making them ill. They say the mail is causing skin irritation, headaches and nausea, as well as tingling, bleeding and the taste of metal in their mouths.

The symptoms, staffers say, can last up to 24 hours, beginning after they touch irradiated letters and subsiding as long as they avoid contact with mail.

More than 150 congressional staffers have reported feeling sick since authorities ordered the irradiation of government mail to try to prevent a recurrence of last fall's deadly anthrax outbreak.

About 80 postal workers, most of whom process mail at a suburban Maryland facility, have also reported feeling ill after handling mail irradiated for their protection.

"It's unnerving," said Luke Albee, Leahy's chief of staff, who helps sort mail in the wake of the anthrax scare, during which a letter filled with anthrax spores was found addressed to Leahy but was never opened.

Albee said he and other staffers in the office began noticing the symptoms last month, once postal service resumed on Capitol Hill.

"Clearly," he said, "something's going on with the mail."

Initially, some blamed the fumigation of the Hart Senate Office Building, which was pumped full of anthrax-killing chlorine dioxide gas after an aide to Senate Majority Leader Tom Daschle opened an anthrax-tainted letter there. Building managers recirculated air through the offices, and authorities said the complaints declined.

Different office building

But the health complaints have extended beyond Hart - Leahy's office, for example, is in a building that was not fumigated. That leads some investigators to suspect a problem in the irradiated mail.

The Postal Service has declared the mail perfectly safe. Testing by the Environmental Protection Agency has found no excessive levels of any chemicals in any Capitol Hill building since mail delivery resumed.

Federal authorities suggest that the reported sicknesses might be related, in part, to the initial high dose of radiation that melted the plastic in some mail, such as in the address windows of business letters. It's possible, authorities said, that staffers felt sick not from the irradiation process but from the fumes of molten plastic.

The Postal Service said it thinks it has remedied the problem by reducing the radiation exposure for all mail, removing plastic from the irradiation procedure and airing out letters before delivery. Mail treated this way should begin landing on desks as early as this week, congressional aides say.

Investigators have suggested that some of the symptoms might be due to unrelated winter colds and flu. As for the skin irritations, officials speculate that because mail becomes brittle after irradiation, it can absorb moisture from the hands of those who touch it and cause some soreness. The more serious complaints, officials say, in all likelihood have nothing to do with the mail.

"We're not aware of any clinical evidence that associates the irradiated mail with the symptoms that have been reported," said Gerry Kreinkamp, a Postal Service spokesman. "If [mail handlers] feel like they've had an adverse reaction to dry mail, use moisturizer."

Some Hill aides said they remain angered by what they called a blase reaction by investigators.

"It's kind of an odd situation where we're being reassured there's nothing wrong with the mail, but they're also assuring us we're not all psycho cases," Albee said of briefings by investigators. "It's fair to say there are a number of offices who believe they could be acting more aggressively."

Last week, the Office of Compliance, which enforces labor laws on Capitol Hill, began an independent investigation at the behest of Hill staffers. Sen. Charles E. Grassley, an Iowa Republican, also requested a inquiry. A board consisting of several health agencies, under the leadership of the Senate's sergeant-at-arms office, is already looking into the matter.