Between tranquil responses to incoming phone calls at her desk, she speaks anxiously about how she dreads next July when she will "celebrate" her 65th birthday and reach her company's mandatory retirement age.

She has been a secretary-receptionist for the same pharmaceutical company for 20 years, has held jobs of some sort since she was 14, and does not know what it means not to work. She says she is as healthy as people in a Geritol ad.

Congress can save her from having to "fill my time with nonsense," she says, by acting quickly to pass legislation, which is now in its final stages and would protect most private sector workers from forced, age-based retirement until they are 70. Forced retirement at any age for most federal workers also may be eliminated.

No one can say how many workers will, for financial or other reasons, share the secretary's desire to continue working, and therefore no one knows what their impact will be on the unemployment rate or a range of other considerations. No one knows how their decisions might be affected by changes now being hammered out in the application of social security benefits - making it possible for the elderly to work longer or earn more, for instance, and still earn benefits. No one knows even how many elderly already are retiring from one job and then resuming work at another, perhaps part-time.

What is known is that the trend among American workers is toward earlier retirement.

Still, legislation to raise or eliminate the outdated retirement age caught fire this year under a civil rights banner and has burned through Congress with an ease that has left some opponents open-mouthed.

This spritely display of "gray power" is but the beginning of a national awakening to the social and political implications of an increasingly aged population, according to expert observers.

Almost 23 million Americans, or about 10 per cent of the population, are 65 or older, and their numbers are increasing in proportion to the rest of the population. Those in that category, more politically active than young voters, cast almost 16 per cent of the votes in the 1976 general election, according to a survey by the Census Bureau, and those 55 or older cast 31.8 per cent of the votes.

Moreover, unlike some lobbying efforts, "where a congressman will get 7,000 postcards that all look alike," elderly people spontaneously send "real letters with real addresses, and that has much greater impact on a congressman," according to an aide to Rep. Claude Pepper (D-Fla.).

The lobbying energy of older people became clear recently when Commerce Secretary Juanita Kreps proposed raising the age of social security entitlement from 65 to 68, a proposal denounced by Pepper and not related to the retirement bills, Pepper's aide said. "Letters, anguished letters, poured into Congress. Suddenly all those demographics became real people," the aide said.

As chairman of the House Select Committee on Aging, Pepper, 77, has become the leading champion of legislation to end age discrimination, a matter he says "should be of concern not only to those approaching 65 but to every person who plans one day to reach 65."

Several powerful voices from the business, labor, academic, and minority communities have been raised against the retirement legislation on grounds that it is being pushed through without proper study.

"A lot of our companies still can't believe this has happened," said Harriet Hackney of the Business Roundtable, a lobbying organization representing 180 companies such as Xerox, DuPont and Exxon.

"They talk about the clout of the business community," she added. "Well, we're the little fish in the sea at this point." She described the mood of business as one of "concern and bewilderment."

Opponents of the change have warned of dire consequences if large numbers of the elderly decide to take advantage of the new law and continue working. The elderly, opponents say, might rob the young of jobs at a time when the youth unemployment rate is soaring: choke the channels of promotion; retard affirmative action programs for hiring women and minority workers, and add to the costs of some benefit plans.

They also say administrative nightmares would be created for managers faced, for instance, with the need to fire elderly employees they felt had become incompetent.

Sears, Roebuck and Co. estimates that among its own work force, the new legislation would reduce the rate of new hires for full-time jobs by 7 per cent. That estimate, which is dispute, is based on figures showing that almost one-third of Sears' retirement-age employees are staying on the job as long as possible.

"I don't think anyone has examined the utter disgust of those who feel we are shooting our own economy in the foot. This is a classic example of good politics making bad economics," Sears spokesman Jim Ritch said.

"The "last hope" of business now is to retain an amendment that would exempt business executives, allowing them to be retired at age 65 to keep "promotions and resh ideas" flowing, according to spokesmen.

Supporters of the retirement legislation maintain that its impact will be minimal. The Labor Department estimates that nationwide, during the next five years, only an additional 200.000 persons, or about .02 per cent of the total work force, will take advantage of the new law and continue working as they reach 65.

The most commong age of retirement for Americans receiving social security benefits is 62, according to government figures, and the proportion of early retires has been increasing at a rate of 2 to 4 per cent a year.

In any case, the legislation is a matter of principle and individual rights, not numbers, according to its supporters. "If you substitute the world 'woman' or 'black' for 'old person,' you see what charades the arguments (against the law) are," said Valinda Jones of the National Council on Aging.

"If you follow the (opposing arguments) to their conclusion." Rep. Pepper said, "you would lower the age of mandatory retirement until every jobless young person has Stolen an older person's job."

The legislation is seen by many, independent of the work issue, as one way of cracking cirppling myths about old age. According to Steve Skardon of the National Association of Retired Federal Employees, the elderly, employed or not, are "caught in this national image of incompetence and feebleness. They feel they benefit immeasurably from the legislation, even if they are already retired, because it will help dispel those myths."

Opponents of age discrimination have marshalled evidence that explodes stereotyped images of crotchety old people, set in their ways, declining physically and mentally, all because of the aging process. In terms of productivity on the job, for example, the elderly can outshine their young coworkers. The variations are greater within each age group than among different age groups, according to various studies.

Pepper and his supporters also note that entities such as Bankers Life and Casualty Co., the steelworkers' union and 14 state governments have eliminated various forms of forced retirement, apparently without demoralizing younger employees, traumatizing supervisors, clotting promotional channels "with doddering incompetents" or other ill effects.

"We are not a bit troubled by this (proposed law)," said John T. mcGinness, vice president in charge of personnel for Woodward & Lothrop department stores. "Although about half our retirees are leaving before age 65 . . . more and more we see in our personnel office people over 65 who want to work. Many of them have retired from other organizations."

McGinness said there are currently 225 workers 65 or over employed by the company. Some are longtime employees allowed to stay on and others are newly hired. Some work part-time without benefits.

The proposed legislation would not force anyone who wanted to retire to continue working, supporters point out, nor would it protect them from being fired if they are incompetent, whatever their age.

Social welfare economist Dr. Malcolm Morrison of Antioch College sees the legislation as a "trade-off, which recognizes the political strength of this group . . . When you have a shortage of work, as we have, you have to try in effect to divvy up the suffering."

Speaking of about 21 million Americans currently collecting retirement benefits, he added. "It's ridiculous to have that much of your population idle."

morrison and other experts see the move to relax mandatory retirement requirements as a changed to try out some ideas that could lead to increased flexibility for workers in general.

In any case, the legislation seems certain of enactment in some form. A conference committee is thrashing out some major differences between the House and Senate bills. The Senate bill would exempt business executives and tenured teachers and would not take effect until January, 1979. The House bill would take effect six months after enactment and would not exempt executives and teachers.

The House bill also provides elimination of mandatory retirement for most federal workers, who currently must retire at 70. The change is expected to have little impact since, in line with the national trend, federal employees are retiring earlier, according to Civil Service Commission Chairman Alan K. Campbell.

The average age of voluntary retirement among federal workers for 1976 was 61, Campbell said. Only 1.2 per cent: of the federal work force is 65 or older.