AT&T's long-distance telephone access charge is facing a close call in Congress

Until recently, members of Congress were about as likely to vote against Ma Bell as to forget to call home on Mother's Day. But the glory days of American Telephone & Telegraph's lobbying power may already be on the wane. Lately Ma Bell has been handed a series of legislative defeats that threaten to hit her pocketbook. And on Wednesday the phone company faces perhaps its toughest legislative battle.

The House is slated to take up a bill that would block a Federal Communications Commission (FCC) plan to have residential phone customers pay a monthly charge for access to the long-distance network after the coming breakup of AT&T.

Nonetheless, with 1 million employees, 3.2 million shareholders, and operations in almost every congressional district, AT&T still has enormous clout on Capitol Hill.

''AT&T's resources are enormous, they use them effectively, and one can never discount the final effect that they will have,'' says Robert Nichols, legislative and regulatory counsel of Consumers Union, which opposes AT&T on access charges.

But he adds that ''there is some evidence that AT&T's propaganda campaign against this legislation is less effective than a similar campaign (against a different bill) a year ago.''

Congressional aides say the company has not generated the avalanche of constituent mail which often accompanies successful lobbying campaigns. For example, Senate Commerce Committee chairman Bob Packwood (R) of Oregon, who was author of the Senate bill blocking residential access charges, has received only 800 pieces of mail supporting AT&T, compared with 30,000 pieces he received earlier this year from advocates of the American Bankers Association position objecting to withholding on interest and dividends.

And in late October, the company lost several key votes in the House Energy and Commerce Committee on access charges for residential customers and on the level of fees paid by AT&T's long-distance competitors for hooking up to the phone system.

''As compared to anyone else their power is awesome,'' a key House Commerce Committee aide says. ''As compared to whether it is as double awesome as last year, I don't know.'' Last year AT&T lobbying caused the House committee to drop a form of breakup legislation (HR 5158) which the company vehemently opposed.

''We are beginning to see the first expression of a less powerful . . . Bell System with this legislation,'' says Eugene Eidenberg, senior vice-president of governmental affairs at MCI Communications Corporation, an AT&T competitor in the long-distance business.

The outcome in the House ''is a very close call,'' says Samuel Simon, executive director of Telecommunications Research and Action Center, a Washington, D.C.-based consumer group. Congressional sources agree.

A number of factors have diminished the company's clout, opponents say. Fighting access charges for residential customers is seen as an appealing political stance. And the risk of such action is diminished because two key phone company unions, the Communications Workers of America and the International Brotherhood of Electrical Workers, both support the bill. Finally, the current measure is less sweeping than last year's communications industry bill and thus generates less opposition.

AT&T officials say the Jan. 1 divestiture of the local phone companies may reduce the company's political power. AT&T ''will remain a very large company but not as large as it was,'' says spokesman Pic Wagner.

''That monolithic power may have been more perception than reality,'' Mr. Wagner says.

He says recent setbacks in the House can be attributed to the ''politically partisan'' approach the Commerce Committee took. ''There is a vendetta against AT&T because of what is perceived we did on [last year's telecommunications bill ].'' But the legislation will hurt the American public, rather than AT&T, Mr. Wagner maintains.

Of course, Ma Bell has not given up.

''AT&T is making a massive effort, they are pulling out all the stops,'' Mr. Simon says.

For example, the company has brought scores of local phone company executives to Washington. ''Every member of Congress has someone assigned to them,'' a House Commerce Committee aide says. ''We don't send total strangers in,'' says AT&T's Mr. Wagner. ''We send someone from that congressional district.'' Since local phone company officials are active in civic affairs, they are not ignored.

In addition, AT&T has spent more than $2 million writing to shareholders and running newspaper advertisements arguing its case.

There is no firm schedule for Senate action on access charges, which, under recent FCC action, are slated to go into effect April 3. In late October Senate majority leader Howard H. Baker Jr. (R) of Tennessee said access-charge legislation would not be brought to the floor until early next year. But Senate Commerce Committee sources say that if the House acts this year, Senator Baker will consider full Senate debate still this year.