Constituents are sending members of Congress more mail than ever, according to a new study, leaving staffers working furiously to respond to the flood of letters and emails.

Congressional offices are receiving between 200 percent and 1,000 percent more messages from constituents than they were 10 years ago, the nonpartisan Congressional Management Foundation's report "Communicating with Congress: How Capitol Hill is Coping with the Surge in Citizen Advocacy" shows.

Senate offices reported a 548 percent increase in mail volume since 2002, and one office said it had shot up 1,422 percent. In the House, the increase in mail was 158 percent.

That influx of messages - the nonprofit CMF estimates the bulk comes through advocacy campaigns - has caused some offices to spend more time than ever before on crafting and sending responses. A majority of staff, or 58 percent, said they spend more time on constituent communications than they did two years ago, and 46 percent report they shifted resources to the mail operation to try and handle the increased volume.

With more people using the Internet and email as the way to get in touch with their representatives, most offices reported they are improving their use of technology compared with where they were five years ago.

Now, 86 percent of offices answer all or most of their email with an email, compared with just 37 percent that did so in 2005. But 6 percent of staffers report their offices are still far behind the times - they do not reply with email to any of the email messages from constituents.

Despite the deluge of messages, Congress has not upped the number of staffers reading and responding to them. Staff size in personal offices has not increased since 1979, the CMF wrote, and constituent mail is an increasing burden on staffers' time. Almost half - 42 percent - said it takes more than three weeks for the office to draft and approve a response to a new issue, and 41 percent report that more than a week goes by before they respond to an email even if something has been prepared and approved in advance.

"[The] CMF's research also suggests that 'old school' habits on Capitol Hill are inhibiting the potential for Congress and citizens to have a more robust, active and meaningful relationship using online technologies," the study's authors wrote. "While responding to constituent communications is a high priority for congressional offices, a sizable number of offices are unable to respond to constituent emails with pre-existing responses in less than a week."

The CMF conducted the survey from Oct. 12-Dec. 13, 2010 and had 260 respondents, with 72 percent from the House and 28 percent from the Senate.