"My father many years ago--God rest his soul--told me that the people running AT&T are much better people than are in the government. Now I believe it. You don't know what you are doing . . . " --Retired Bell System employe

The letters come in each day by the boxful--angry, insistent, occasionally heart-rending.

By some Senate and House members' reckoning, they constitute the most massive outpouring of mail on a single subject to hit Capitol Hill since the Saturday Night Massacre at the height of the Watergate scandal.

American Telephone and Telegraph Co., a corporate leviathan that lately has been feeling hectored by the courts, bullied by the Congress and one-upped by its competitors, has decided no more Mr. Nice Guy. For the first time in a long history of congressional lobbying, it has decided to unleash its 3 million shareholders and one million employes on Congress.

The first wave of mail--most of them form letters--has just begun to land. Rep. Matthew Rinaldo (R-N.J.) says he's gotten 12,000 pieces in the past 10 days; Rep. James Florio (D-N.J.), 10,000. Both are members of the House Energy and Commerce Committee, which next month will consider HR 5158, a bill that would impose stiffer restrictions on Ma Bell than the terms of an antitrust settlement the company made with the Reagan administration in January.

AT&T charges that these restrictions threaten its financial health as well as the future viability of its 22 local operating companies, which will be split off from the Bell System under both the court settlement and the bill.

"Your investment, your savings are at stake," says the dire letter that AT&T Chairman Charles L. Brown sent to shareholders, calling on them to write members of the House committee. "If the quality and price of phone service is important to you, read on," says the bill insert Mountain Bell is sending to its customers, urging them to write their congressmen against HR 5158.

"HR 5158 is a wrong number," say the buttons Bell has distributed to its employes.

AT&T is spending about $2 million to boost its cause, spending large sums on nationwide advertising and letters to shareholders. Even though they are to be split off from AT&T, the 22 local operating companies have eagerly joined the battle, holding press conferences around the country, running advertisements prepared by the Bell System, and sponsoring employe rallies--all in an effort to get their employes and stockholders to write Congress.

Is the grass roots lobbying blitz making a difference? Congressmen do count their mail, of course, but they also count how much of it is generated by special interests. To some, the whole effort smacks of overkill.

One skeptic is Rep. Al Swift (D-Wash.). On Monday, his office received 600 letters opposing HR 5158, but 500 of them were from out of his district and many of those were from out of state. "AT&T is throwing a corporate temper tantrum," he said.

Whatever the effectiveness of the campaign, the tactics themselves suggest a feistier lobbying tack for the Bell System. It has long been considered a powerhouse corporate persuader, but in the past its methods had always been low key and discreet.

Now AT&T says it's been forced to adapt its lobbying style to the new aggressiveness of its competitors. The company is particularly incensed at a pro-HR 5158 mailing that went out in late February from the National Coalition for Fair Rates and Competition.

The envelope that contained that mailing read: "Notice of Telephone Rate Increase Enclosed," and next to it was a circle with a phone inside it, an insignia apparently intended to be confused with the AT&T bell it closely resembled. The letter warned that phone rates would double, and that Bell would be permitted to stifle fledgling competition in the telecommunications field unless HR 5158, sponsored by Rep. Timothy Wirth (D-Colo.), was passed.

That mailing, which went out to 180,000 selected homes, generated 35,000 return letters to members of Wirth's telecommunications subcommittee, which last month voted 15-0 to support the chairman's bill.

Bell insists the letters were the lowest form of fear-mongering. The coalition responds that Bell is doing the same thing with its missives.

And the mail wars haven't been all one way, either. Rep. Thomas J. Tauke (R-Iowa), a telecommunications subcommittee member, reports getting 6,000 pro-5158 letters and 1,500 against.

Some subcommittee members worry that both sides in the mail wars are playing fast and loose with the facts, distorting the terms of a debate that for the general public is still in its infancy.

"The people who write you and call you are very sincere," says Rep. Thomas Bliley (R-Va.), "but most of them do not begin to have the information that the subcommittee does."

That doesn't suggest the letters are for naught, however. Bliley adds: "At the very least, the outpouring is going to force the rest of Congress to get up to speed on the issues mighty fast."