During the muggy nights of early last September, the underground corridors near the Rayburn House Office Building echoed with the clackety clack of printing machines as workers rushed to get members' newsletters finished before the deadline for election-year mailings. Among the head-high stacks of mail that lined the basement corridors was a mailing prepared by Virginia Republican congressman Stan Parris.

The letter was titled "Setting the Record Straight" and was sent to 160,000 households in suburban Virginia's 8th District at a postage cost of $32,000. The newsletter was designed to correct, it said, "a number of misstatements or distortions concerning my votes on issues of importance to the people of Northern Virginia." The "misstatements and distortions" brought a sense of deja vu to Virginia State Sen. Richard Saslaw, Parris' opponent in the 8th District race. Most of the issues being rebutted were those Saslaw had raised in the campaign.

"That was strictly a campaign piece. He didn't pretend on that one," said Saslaw, who believes Parris' ability to send free mail was "the key factor" in his losing the race. Parris says that although he was responding to issues raised by Saslaw, "the purpose of it all was to inform our constituents."

Two constitutional principles butt heads over the issue of Congress' free mail perquisite, also known as the franking privilege. On the one hand is the necessity to communicate with constituents, a lifeblood of democracy. On the other hand, challengers must be able to engage in a fair fight during an election.

What the Founding Fathers did not anticipate when they scrawled out the franking privilege with their quill pens was how the computer would multiply by a thousandfold the ability of legislators to send mail.

In 1984, House and Senate members sent out more than four times as much mail as they sent in 1970. The blitz of 924 million pieces of mail last year was at least 60 percent of the volume of nonfranked mail that went out of Washington last year.

Total postage for the House and Senate for fiscal 1984 was worth $111 million, slightly less than the Peace Corps budget that year. House clerk Benjamin Guthrie recently estimated the bill for fiscal 1986 will top $144 million for a recordsmashing 1 billion pieces of mail. "God help us," said Rep. Andrew Jacobs Jr. (D-Ind.), "You won't be able to tell whether it's snowing or not in the country by that time."

STAN PARRIS is "one of the more aggressive mailers" in the House, according to his press secretary Dick B. Leggitt. During the last session of Congress, Parris sent out about a million more pieces of mail than the average congressman. That was enough mail to form a stack of letters at least double the height of the Washington Monument -- 3 million pieces in all, roughly 14 pieces for each person who voted in Parris' district last November.

The average piece of franked mail cost 121/2 cents to mail last session, which means the cost to taxpayers for postage on Parris' 3 million pieces was about $375,000, or $1.30 for each registered voter in his district.

Although Parris is now taxing the maximum capability of his equipment to put out personalized mailings, faster laser printers will become available to House members within the year. "We're limited solely by the amount of speed at which the computer can generate the mail," Leggitt said. "We're starving for a faster printer."

COMPUTERS ARE GOOD at organizing information and putting it on paper. They are also very good at being selective. They are ideal for congressmen who want to communicate special messages to select parts of their constituency. For example, the computer in Parris' office stores 200,000 names and addresses. Another 200,000 are stored for him in the large computers of a Silver Spring firm called ITT Dialcom Inc. The computer has broken down the names and addresses into 1,392 lists.

Some of the lists are of key contacts in Congress and the federal government, but most are lists of 8th District constituents grouped by categories for targeted mailings.

It's quite easy to get listed in Parris' computer. Did you visit or phone Parris' office or attend one of his town meetings? Chances are your name and address were obtained by a friendly staffer and logged in. Did you write a letter to Parris expressing concern about U.S. involvement in Nicaragua? Did you sign a petition protesting noise from Washington National Airport? Your name could be in Parris' data base along with your position on an issue.

Are you a veteran? Parris' office requested a list of veterans in his district from the Veterans Administration. Are you a teacher? Your name was obtained from local education directories. Are you a small businessman? The National Federation of Independent Business gave your name to Parris. Did you respond to Stan Parris' annual issues questionnaire? Your name, address and position on key issues went into the congressman's electronic files.

Are you a federal employe? Your name and the names of 20,000 other federal employes were obtained through questionnaires and from letters and form Parris' biggest single list. If your Zip Code places you along I-396 or the Potomac River, or near Lorton Prison, you may be on the list that gets a mailing on transportation, airplane noise or on Parris' efforts to get the prison moved back to the District.

Incoming mail and questionnaires provide the bulk of the names that are associated with issues. The lists include people who are concerned about everything from Libyan terrorism to gypsy moths to rabies. Parris keeps a list of those who favor the MX missile and a list of those who oppose it, same for the B1 bomber, the nuclear freeze and space research.

By applying computers to state lists of hunting and fishing licenses, a congressmen could sort out all the blue-eyed 18- year-old turkey hunters. "The possibilities (for developing lists), as you can see, are endless," says the National Republican Congressional Committee in a manual given to new GOP congressmen.

Throughout 1984, Parris' constituents were peppered with mailings as his computer churned out "personalized" letters at the rate of 1,200 a day, provided a staffer would come in at 2 a.m. to change the typing ribbon. The mailings included:

*People who had written to Parris on environmental issues received at least eight letters last year from the congressman. Usually the letter began, 'Knowing of your interest in the environment . . . " and continued with Parris' achievements in that area. People who, in response to a 1983 Parris questionnaire, said they disapproved of James Watt, then Interior secretary, got letters pointing out selected votes on which Parris had supported environmental issues in opposition to Watt. Parris, however, voted only once out of 14 times in support of environmental issues in 1983 according to the League of Conservation Voters, an environmental group. "I think he flunked," a League staffer said of his rating.

*About 6,000 people who had indicated by letter or questionnaire that they were opposed to Lorton Prison got letters telling of Parris' efforts to get the District's prison out of Virginia.

*"Knowing of your interest in . . . " letters went to educators, to people who had written about child nutrition programs, to veterans, government employes and others.

*To an Alexandria woman who had written to Parris opposing the MX missle: "Rest assured that I will give future MX funding especially hard scrutiny," the congressman replied. But those whose letters or questionnaire responses marked them as more hawkish got letters beginning: "Knowing of your support for a strong national defense . . . " The letters went on to highlight Parris' support for the MX missile.

The "Setting the Record Straight" letter that Parris mailed to registered voters three months before the election rebutted three "misconceptions" regarding the congressman's position on retiree benefits, reduction of the federal deficit and the Washington subway system. Where did the issues originate? "Obviously," said Parris, "from the guy that ran against me."

Did the mailing help his reelection campaign? "I certainly hope so," said Parris.

Does the mailing constitute public funding of his campaign? No, says Parris. "What the purpose of it is is to inform our constituents of our position in an accurate way."

Before mailing the Setting the Record Straight newsletter, Parris' aides submitted it to the House Commission on Congressional Mailing Standards, chaired by Morris K. Udall (D-Ariz.). There, as is customary, both Democratic and Republican aides reviewed it to determine whether it passed the test of political fairness. It passed.

"I didn't find anything that violated any franking rules," said minority staff director Joseph A. Fisher. Udall, after reviewing the mailing, called it "questionable at best." The franking privilege, Udall said, "was not intended for the purpose of correcting misstatements and distortions raised by an opponent."

Parris won the election by 26,285 votes in the traditionally Democratic district that he'd won in 1982 by 1,559 votes. Opponent Saslaw says Parris' franking privilege freed up campaign money for other uses such as telephone solicitation. A comparison of the two candidates' campaign expenditures shows Saslaw spent about 24 percent of his campaign funds on mailings ($84,000 of his $350,000 campaign budget). Parris spent about 9 percent ($63,000 of his $700,000 budget). Saslaw's printing costs were 16 percent of his campaign budget; Parris' were 4 percent. "I would have spent another $250,000 on mail if I'd had it," Saslaw said.

An informal survey of voters as they left the polls at several locations in the 8th District last Nov. 6 showed Parris' mailings may have been effective. Of 80 people interviewed, 70 recalled getting mail from Parris in the last year. Only 37 recalled getting mail from Saslaw.

Some voters surveyed said Parris' mail was a decisive factor. "It made a big difference," said a 20-year-old Northern Virginia Community College education major who did not wish to be identified. The student said Parris mailings on public transportation won her vote. "You know he was really interested in what was going on," she said.

Others scoffed at the impact of the mailings. "I think he should save his money on mail," said Doug Glynn, 26, an Alexandria assessment clerk. "I feel we get a pretty good idea of how he stands from other sources."

THERE ARE FEW PEOPLE on Capitol Hill who say that the franking privilege is not used for reelection purposes. House and Senate mail volume nearly doubles from nonelection years to election years. "(House Speaker) Sam Rayburn used to say there were three keys to getting reelected," Udall recalled: "Use the frank, use the frank and use the frank."

Kent State University political scientist Murray Fishel estimates the value of the frank to be between $350,000 and $750,000. Says Fishel, who is a frequent consultant on political campaigns, "If you're running against an incumbent, you start out with zero dollars and your opponent starts out with $350,000. Add in staff, lists of people who have contributed to them before and so on and it becomes an enormous advantage."

The National Republican Congressional Committee manual tells nw members that "few things are more powerful than a personalized, well-written letter on an issue that directly affects the reader." Under "Utilization of Government Perquisites/Allowances" in the manual is this prod: "Do you maintain a count of mail leaving your congressional office? If so, are you showing a steady increase in the number of letters you mail?" A sampling of 1984 mailings reveals such suggestions are not going unnoticed:

Rep. Michael Barnes (D-Md.) sweetened his newsletters with photos of him accepting a poster in honor of Maryland's 350th anniversary celebration. His Democratic colleague from Maryland, Rep. Beverly Byron, printed pictures of herself climbing aboard a Navy A4 for a

practice flight with the Blue Angels,

posing with Marines in Grenada and

touring Racal Communications Inc.

in Rockville. Sen. Rudy Boschwitz

(R-Minn.) used a picture of himself

in front of the milk machine he had

installed in his Senate office; in a

letter to women, he included a

picture of himself with Sen. Nancy

Kassebaum (R-Kan.) whom he

called "one of my closest

colleagues." Last August, some

1,000 Iowans with abbreviated

intestinal tracts were the target of a

mailing from Republican Sen.

Charles Grassley notifying them

that the senator was "happy to take

part in the passage of the 'Ostomy

Awareness Month' resolution

because I feel it is an important

piece of legislation. You are a

special group of people who deserve

recognition and commendation."

Such selective communication

"removes public debate," said Don

M. Boileau of the Speech Communication Association, an association of communication academics. "If direct mail takes over on a selective basis, you aren't going out into public where you can be challenged. Even if the opponent had the resources to respond by mail, he doesn't even know what the charges and countercharges are. You don't have to develop a total picture, you don't have to meet the public in a responsible communication environment.

In an effort to discourage senators from sending too much mail, the Senate Committee on Rules and Administration last month passed a rule that would make public the volume and cost of each legislator's mail. "Each time American citizens receive unsolicited congressional mail they should be on notice that it is costing them money," said Sen. Charles McC. Mathias (R-Md), the author of the provision.

ANDREW JACOBS is one of the few members of Congress who do not use the frank to send unsolicited mail. "We're getting deeper and deeper and deeper into plastic politics," said Jacobs, who would like to see newsletters eliminated. "I don't know how many congressmen or senators you have saying it's terrible to give a baby a little milk through the WIC (Women, Infants and Children nutrition) program and who at the same time engage in the frank at public expense."