What was going on when I was born?

The Brazilian Government and an International Monetary Fund negotiating team agreed today on a $4.5 billion credit that Brazil had urgently sought to keep up with payments on its huge foreign debt. Under the terms of a letter of intent signed here this morning, the credit could rise to $6.7 billion over the next three years, according to Carlos Geraldo Langoni, president of Brazil's central bank. That would happen if the I.M.F.'s member nations increase their contributions to the lending agency by 50 percent, as seems likely next year. The increase would add more than $40 billion to the I.M.F.'s treasury. That treasury is being quickly depleted as a result of the credit agreement with Brazil and similar agreements in the past six weeks with Argentina and Mexico covering more than $6 billion in credits. Those three huge credits leave the I.M.F. with only about $10.6 billion to lend, according to monetary officials.

The trucking industry, already shaken by profound changes in the regulatory climate and the depressed economy, is convinced that pending tax increases on heavy trucks will drive many marginal operators out of business and help speed up the diversion of shipped goods from trucks to railroads. Truckers have lobbied strenuously against the tax increase measure pending in Congress, and independent, self-employed truckers are threatening strikes if the higher levies are passed. The new taxes on fuel, tires and trucks would largely be passed on to customers despite strong existing competition because industry profits are low, trucking officials contend. The higher relative cost of shipping by truck should favor the railroads, which have been competing more actively in recent years, trucking and rail officials agree.

The Senate Appropriations Committee voted a tough new restriction today on President Reagan's ability to buy MX missiles. The limits go beyond a compromise the President endorsed Tuesday and amount to another setback in the Administration's struggle to win Congressional approval of the missile system. The amendment adopted today, which was proposed by Senator Ernest F. Hollings, Democrat of South Carolina, contains most of the provisions of the compromise. It would appropriate $988 million to buy missiles but would bar the President from spending any of it until both houses of Congress ratified plans for deployment of the weapons. The new restriction is that the amendment does not contain the deadline for Congress to conduct a ratification vote. The President considered that a key part of the compromise.

GREEN and blue and red Christmas lights twinkle around the handwritten ''Happy Holidays'' sign at the Newport Garage at 370 East 76th Street. The sign lists names of customers who have already made their contributions to the holiday kitty. ''This is tipping by intimidation,'' said Stanley Edelman, an American Express business analyst who sometimes parks his car there. ''It's the element of fear involved. If I don't do it, what then?'' Not at all, says the garage manager, James Harris: ''It's just proof that when customers give me their tip it's not going into my pocket. The money is going to all the boys.''

Roy L. Williams, the teamsters' union president, was found guilty with four other men today of conspiring to bribe a United States Senator and defrauding the union's Central States Pension Fund. After almost 27 hours of deliberations, the jury returned guilty verdicts on all 11 counts against each defendant. The verdicts were read to the defendants by Federal District Judge Prentice H. Marshall, who presided over the seven-week trial. Mr. Williams, who is 67 years old and ill with emphysema, was the third president of the International Brotherhood of Teamsters to be convicted of a felony in Federal court in 25 years. Ties to Teamsters Those convicted with him were Allen M. Dorfman, 59, a Chicaco insurance millionaire and convicted extortionist who has long ties to leaders of the teamsters and of organized crime; Joseph Lombardo, 53, a long-time associate of Mr. Dorfman who is a reputed Mafia liaison agent with top teamster officials; Thomas F. O'Malley, 46, a trustee of the pension fund, and Andrew G. Massa, 64, a former pension fund trustee.

For the first time, scientists say they have transplanted genes from one animal species to another and effected profound changes in growth. Mice were given rat genes and grew to twice their normal size. Collaborating scientists from four major institutions transplanted a specially modified gene for rat growth hormone into fertilized mouse egg cells, which were then implanted in foster mother mice, it was reported. Some of the mice born from these experiments produced huge amounts of the foreign growth hormone and grew at faster than normal rates.

SMART babies are curious babies, and the larger the space they are allowed to roam, whether indoors or out, the more exciting are their lives. Dr. Burton White, author of ''The First Three Years of Life'' and the director of the Center for Parent Education in Newton, Mass., said: ''If you prevent a child from moving around and use playpens and jump seats, you inhibit the child. To see people is a thrill. To find a piece of cellophane on the floor makes him delirious. By putting fancy antiques on tables and telling children not to touch them, people justify themselves by saying that the children will learn about no. But the child associates 'no' with the object and curiosity, so you teach him that what he's going after is bad.'' To raise a curious child, parents have to baby-proof their home so that it is at once a place for exploration and safe from danger. In 1981, the National Safety Council estimates, 2,200 children, from newborns to 4-year-olds, died in accidents in the home. The causes of death included fire and burns (650), drowning in tubs or swimming pools (350), suffocation by ingested food or object (300), mechanical suffocation by bedclothes or plastic bags (250), falls down stairs or against hard objects (150), poisons by solids or liquids (80), poisons by gas or vapors (70) and firearms (50). Other accidents involved electricity, explosive materials and hot substances.

International Brazil is to receive $4.5 billion in credits over the next three years under an agreement reached by its Government and a negotiating team for the International Monetary Fund setting the conditions for the credits. The credits, which could rise to $6.7 billion, are designed to help Brasilia resolve its liquidity crisis. (Page A1, Columns 3-4.) Spain assured Washington that it would remain a loyal ally even though its new Socialist Government has ''frozen'' the country's further integration into NATO. The pledge was made to Secretary of State George P. Shultz by Prime Minister Felipe Gonzalez. (A11:1.)

First of two articles on the changing telephone business. The way in which Americans have obtained their home telephones for decades is about to undergo a major change as the telephone industry enters a new era. In coming years, more and more people will be buying telephones from stores and catalogues at unregulated prices rather than renting them from the phone company at rates set by the states. In short, people will obtain and repair telephones much as they now select toasters, televisions and other household appliances. The change will force millions of people to make decisions about something they never had to think much about before. And of all the developments in the telephone industry occurring as a result of the breakup of the Bell System and other Federal regulatory actions, the change in the way telephones are provided is likely to be the most evident to consumers.

Brazil and an I.M.F. team agreed on a $4.5 billion credit that the country has urgently sought to keep up payments on its huge foreign debt. In return, Brazil has agreed to continue its austerity program. (Page A1.) It is also expected to ask foreign banks for about $5 billion in new loans and about $4 billion of refinancing. (D6.) As the list of countries seeking short-term emergency cash from the Bank for International Settlements grows, the central bank institution is becoming uneasy about its role and abilities. (D6.) Steelmakers will ask the U.S. to curb Japanese imports by onethird. An unfair trade petition to be filed today asserts that American producers have been hurt by secret market-sharing agreements between Tokyo and the Common Market. (D4.)

Like most of the nation's consumers, Sherril Booth says she was more price-conscious than usual in her gift shopping this year. ''Everyone is a little more concerned about money these days,'' she said the other day. The frugality, however, did not extend to the airline tickets she bought last week for a Christmas trip to Detroit. ''You have to go home for Christmas,'' she said while making her reservations at the American Airlines office at Rockefeller Center, ''and worry about the bills afterwards.''

The House, after long debate, passed tonight by a narrow margin a protectionist trade bill requiring foreign auto manufacturers selling cars here to use substantial percentages of American parts and labor in their vehicles, as well as use American advertising services. The measure was passed by a vote of 215 to 188. The measure, which is aimed at Japan, is intended to encourage foreign auto makers to build their cars here, thereby creating jobs in the ailing domestic automotive industry. Slim Chance for Senate Passage Although the bill is given almost no chance of passage by the Senate, the House action was considered highly important because it reflected American frustration at the slow progress Japan has made in opening its markets to a variety of American goods.