Jean Tharp's life changed this week. She started working seven hours a day at a Gaithersburg car dealership, instead of five. She started bringing home almost $90 a week, instead of $56. She and Yvette, her 11-year-old daughter, will now learn what it is to live without government help.

Last week, on the eve of the new fiscal year and the beginning of reduced welfare benefits for millions of Americans, Tharp received a letter:

"Your check for October, 1981, is canceled. Your medical cards are also canceled. Please return them in the enclosed envelope. Your gross monthly income exceeds 150 percent of the state's need standard." Tharp's food stamp allowance was cut from $123 a month to $105, and she was told to expect further reduction.

Tharp, a 34-year-old Gaithersburg resident, earns the minimum wage of $3.35 an hour on her job as a clerk in the car dealership office. Her wages were supplemented by $216 monthly from Aid to Families With Dependent Children (AFDC), the major welfare program. The Maryland standard of need for a two-person family such as Tharp's is $211 per month, so although she was taking home only $56 a week, her gross monthly income, before tax and Social Security deductions, topped 150 percent of the standard by nearly $30. Eligibility for federally funded programs is based on need standards set by the states.

Tharp lives in a $395-a-month apartment with her daughter and Steve Ray, an apprentice carpenter, who pays half the rent. Tharp couldn't afford it without Ray. He paid all the rent for October because Tharp didn't have the money on hand. "I told him I will come up with all I could," she said. "He knows it's not my fault."

Right now, Tharp's biggest problem is fear. If she never comes up with the rent money, she said, she'll have to leave, and she fears she will not be able to find a new place she can afford. "Welfare says there's nothing they can do but take away my kid, if that happens," she said.

She is also afraid for her daughter. Yvette has needed frequent medical care for ear and throat problems in the past, and Tharp fears the little girl will continue to need a doctor's care often. Without Medicaid, Tharp will not be able to pay the bills.

"Now I have no idea of what I'm going to do. If I start working more, I'll lose everything," said Tharp. "It's not so bad if you have at least a little bit of money. I feel like I've lost my mind. I cry constantly. I just don't know what else to do."

Tharp is not alone. In Montgomery County, 21 percent of AFDC recipients -- 1,848 persons -- were dropped from the welfare rolls or had their benefits reduced. Of 482 families in the Earned Income Credit Program, which gives tax credits to low-income earners, 275 have been cut and 140 saw their benefits reduced. Another 140 families will be cut off by February.

By counting the income of step-parents as part of household earnings, another new requirement, 102 families will lose at least some welfare benefits. Fifteen pregnant women no longer can draw AFDC benefits for their unborn children, and 135 are receiving less.

For 521 families, including Tharp's, food stamps were reduced or canceled, and further reductions are expected.

In the Prince George's Social Services Department, the staff is still trying to catch up with the paperwork, said June Fisher, deputy director of the income maintenence office, which administers most welfare programs. So far, the number of people affected by the new rules can only be estimated. At least 900 persons have been dropped from AFDC programs, and the benefits of 200 others have been reduced. More names will be removed from the rolls when the paperwork is done.

About 615 expectant mothers will lose benefits for their babies. Some 700 people have been cut from the Earned Income Credit Program. The number of people losing food stamps has not been calculated.

To Tharp, the figures are confusing and frustrating. She still isn't sure precisely what she has lost, what working more hours will mean, or what she will lose in the future. She says she wants to move to a less expensive place, but a year's lease has been signed and she cannot move far from her job because she has no car. More than 6,000 persons are awaiting public housing in Montgomery County.

Tharp has little of value. She sold her jewelry, worth about $60, to rent a campsite for a summer vacation. She owns running shoes and a pair of slippers, but no shoes or boots. She has no dresses. Her television set is in a repair shop and she cannot pay the $47 bill to get it back. She owes the telephone company $22. She has no bank account. "I wouldn't have anything to put in it," she says. Yvette will not be able to go with her class on a camping trip because her mother cannot afford to send her.

Life has not always been easy for Tharp, and sometimes she has made it harder for herself. She left home, pregnant, at 18. She has been married, and divorced, three times. Her last husband, Yvette's father, has disappeared and the authorities have given up their efforts to find him and extract child-support payments.

But this is the first time she has felt truly afraid, Tharp said. "I feel like someone's got me by the throat. I'm not sleeping, I'm losing weight."

When she received notice that her aid would be cut within two days, she put her daughter to bed, drank a fifth of liquor and was sick. "My problems were still there in the morning," she said. She panics when she hears bad news. When she heard President Reagan's Oct. 1 press conference, in which he said he would hold firmly to his economic program, she broke down and cried.

"There have been times when I thought it was bad," Tharp said. "But things have never been this bad." The difference now, she said, is that there doesn't seem to be any way out of her problems, and no one to answer her fears.

Even social service workers, who in the past have offered hope and consolation to people like Tharp, say they have little to offer now.

C.D. Lester, director of income maintenance with the Montgomery County Department of Social Services, said he is skeptical about the value of the reductions. "They cut the incentive to work and that's bad," he said. "I think this is going to have a serious impact on so many people."

Fisher, the deputy director of income maintenence in Prince George's, said she can offer no hope to people like Tharp. "I don't know what's going to happen to them," she said. "Mothers won't be able to make it. I think maybe something had to be done but this was a little too stringent, especially in this state, and especially in the Washington area."

"How do you expect people to live?" Fisher said. "Persons on welfare in this area are truly at a great disadvantage" because of the high cost of living and a standard of need that Fisher described as too low and out of date.

Said P.G. social services spokeswoman Kitty Heuper, "We forsee a lot of suffering."

Thus, when Tharp went to ask her social worker for help and advice, she found none. "I asked him if he had any suggestions as to where I was going to get the money for the rent, where I was going to live. He said he had no idea." He gave her the telephone numbers of her congressmen and senators and the number of the White House switchboard.

When she returned to apply for a medical card she was told she could not get one unless she earned less than $248 a month. Tharp said the supervisor she spoke to asked, "How can you live on $248 a month?" When Tharp asked the comptroller where she works how she could get medical insurance, she said he told her she was making too little money to be able to afford it.

"I'm stuck," Tharp said. "If they had given me a month's grace period I might have been able to rearrange things. But no. They gave me two days."

Tharp says she knows things could be worse. For now, she has her apartment and enough to eat. "I'm not one of the 'truly needy,' " she said. "There are other people worse off than me. But my daughter is truly needy. She's the one who's deprived."

Where her hopes lie, Tharp doesn't know. "I had a dream the other night that I won a million dollars," she said. "And do you know what I did? I hid it." CAPTION: Picture 1, Jean Tharp and daughter Yvette in their Gaithersburg home.; Picture 2, Jean Tharp was notified that her income of $56 per week was too high for her to continue recieving aid for her daughter. Her food stamp allowance has also been cut.