WHAT WILL happen on Oct. 1 when most of the $35 billion in budget cuts voted by Congress last July go into effect? It depends on who you are and, crucially, on where you live.

Some kinds of people will be hurt wherever they are. If you are one of the holders of last year's 350,000 CETA jobs, you will be laid off--if you haven't been already. If you are a welfare mother with a job, your family will lose some and perhaps all of its supplemental welfare aid, food stamps and perhaps Medicaid coverage as well. You may also find a caseworker at your door wanting to enumerate your possessions to see if they exceed the newly lowered limit on such holdings. If you are from a low-income working family not on welfare, your food stamps will be reduced, and you may also find that Medicaid will no longer help you if you face very large medical bills. How fast this will happen depends on how long it takes the welfare office to process your case.

If you are a schoolchild, you are probably already eating a poorer lunch--those cuts went into effect this month--unless your school district is wealthy enough to make up for the lost federal aid. If you are applying for a government loan for the next college term, you will find interest rates up and new income limits in place. If you are out of work, there will be less help in training for and finding a new job and new limits on benefits for the long-term jobless.

Small businessmen and farmers will start finding it much harder to get government loans. Travelers will find their opportunities further reduced--starting Oct. 1, Amtrak will cut service by about 10 percent, and some routes will be discontinued. Other effects, however, will be slow to develop.

Most education programs won't be hit until a year from now, since they are funded a full year ahead. Housing and other economic development programs usually have money in the pipeline so they won't slow down right away. Gradually, however, waiting lines for low-income housing will grow still longer, maintenance of roads and community facilities will lag, and fewer ports will be dredged.

In other programs like daycare, services for the elderly and community health, states will find it hard to translate the big federal aid cuts into immediate reductions in service. In many areas these programs are already suffering from local budget cuts and the loss of CETA workers so that further layoffs of workers may be delayed in the hope that other sources of help can be found. This may mean an even sharper drop in service later in the year to make up for overspending, especially if the administration obtains the further cuts in 1982 spending that it is now seeking.

How much hardship all of this produces will depend on the ingenuity--and wealth--of each state and locality. In areas benefiting from the energy boom, primarily the West and upper Midwest, heavy taxes on oil, coal and other mineral resources and general prosperity will make it easy for states, private industry and philanthropy to fill the gap. New flexibility in a few programs may also help states to concentrate remaining federal aid on the neediest localities. But about half the states, hurt by the continuing slump in basic industries and locally imposed limits on taxes and spending, will find it hard to maintain present commitments, let alone to compensate for lost federal revenues.

In other words, if you are personally well-fixed or live in a prosperous area, you are not likely to find the first round of the budget cuts hard to live with. But if you or your community are already in trouble, your trouble will likely get worse. Isn't that nice?