This was the day Timothy F. Maloney had been anticipating ever since his 12th year, when he worked as a "gofer" on Capitol Hill and began plotting the course that led to his swearing in today as the youngest legislator in the Maryland General Assembly.

Maloney studied his political father for years. He organized petition drives. He worked on dozens of campaigns. He cheered when his hair started falling out prematurely, convinced that baldness would make the voters think him more mature than his years. And this afternoon, his goal reached, the 22-year-old delegate from Beltsville, shut the door of his legislative office and popped open a can of beer.

The clamorous first day, the fast mixing of veteran politicians, lobbyists and relatives, did not hold the same excitement for Maloney's fellow Democrat, Sen. Frederick C. Malkus, Jr., who has seen it all before in his 32 years here -- the longest stretch in the legislature. After breezing through the ritualistic swearing in to his ninth legislative term, he withdrew for a day of trapping muskrats on his 400-acre farm on the Eastern Shore.

Before he left town, the 66-year-old Malkus, who is known as the "silver fox" because of his generous mane of white hair, delivered a speech of the type that has built his reputation as the most vocal rural conservative in the legislature. Bemoaning the increasing influence of metropolitan areas, he said he has attended only one Baltimore Oriole game since reapportionment robbed the "country boys" of their power and gave Baltimore the largest delegation in the State House.

"Somebody gave me a ticket to the World Series," he recounted on the Senate floor after today's swearing in ceremonies. "I went, I was really enjoying it till the second or third inning. Then I saw that Chief Justice of the Supreme Court, Mr. Earl Warren (the liberal jurist), sitting behind me, and that 'bout ruin't it for me."

These two men, Malkus and Maloney, in a sense served as symbols for the opening day of the 1979 legislature. Malkus, the oldest of the old guard, was a reminder of Maryland before reapportionment while Maloney is one of the 63 new delegates and senators who represent the largest freshman class in the General Assembly's recent history.

This new legislature will be working with the first new administration in a decade, an administration headed by a man who speaks kindly of legislative independence. Gov.-elect Harry R. Hughes was not even present for opening ceremonies, choosing instead to spend the day with his aides in Baltimore preparing for his inauguration Jan. 17.

The legislature never enjoyed such freedom under Gov. Marvin Mandel, who exercised strict control over the body during his nine years as chief executive. Until his conviction for political corruption forced him from office last year, Mandel used opening days to invite returning lawmakers to his office for visits and sent forth his legion of lobbyists to renew acquaintances.

Today, Mandel stayed far away from the State House. Many of the friends and politicians who helped him get his way with the legislature for years were there, but they came as visitors, not participants. Acting Gov. Blair Lee III, who was Mandel's lieutenant governor and then served out the final year of his term, circulated in hallways, while past Senate President Steny H. Hoyer forlornly watched the upper chamber from the visitors' gallery. They were defeated for the offices of governor and lieutenant governor, respectively, by Hughes and Samuel Bogley in the September Democratic primary.

John Hanson Briscoe, outgoing speaker of the House, was reminded all too strongly of his new civilian status when he had to find a public parking place instead of the convenient spot outside State House reserved for legislative leaders.

"I used to have the best parking place in the state," he said, "Now the chances are my car will be towed or ticketed."

When he finally reached the House chambers after a one mile walk from an illegal parking zone, Briscoe took his place behind newly elected Speaker Benjamin L. Cardin, who like Senate President James Clark Jr. in the upper chamber, reminded legislators of the voters' mandate in the fall election to hold down government spending and cut taxes.

The rest of the day was consumed with routine first day chores -- adopting rules of procedure, formally voting in new legislative leaders, sending out prefiled bills to various committees and recognizing some of the state's former leaders sitting in the visitor's gallery.

The opening day was more than ceremonial for one man -- Francis W. White, a freshman delegate from Prince George's County. White, a Democrat, went to Annapolis today uncertain whether he would be allowed to take his seat because of a legal challenge questioning his residency in the district from which he was elected.

At a meeting last night, Speaker Benjamin L. Cardin and the rest of the House leadership decided that White should be allowed to take his seat -- with full voting and salary privileges -- while a special committee investigates his qualifications. Most delegates said yesterday that they have no doubt White will be exonerated from the charge that he did not officially live in the 26th district during the election.

"Personally, I wouldn't even have had an investigation," said Del. Robert Redding, chairman of the Prince George's delegation. "I would have been cavalier and just ignored the damn thing. White got more votes than anyone in his district, remember."

Maloney and Malkos also got the most votes in their districts in November -- one of the few things they have in common.

Maloney, although only 22, has been immersed in politics for most of his life. After his remarkably young start on Capitol Hill ("senators put up with my 12-year-old quirks," he says), he began working for the causes of his father, a former county attorney. Father and son railed against the bi-county agencies of Prince George's and Montgomery and organized petition drives to fend off various county tax plans.

As a result of these experiences, Maloney came to the legislature today prepared to act and unwilling to follow the tradition that says freshmen should be seen but not heard. He already has drafted a series of measures -- all aimed at returning the bi-county park and planning commission to county control -- that could be the most important Prince George's local bills of the session.

Maloney's actions have irritated some of the veterans in the county delegation. "I don't understand how a kid like that can get treated so seriously and get his name in the paper all the time," one commented. Maloney takes such criticism lightly and frequently jokes about his balding head, expanding waistline and tender age ("My father's the only guy in Beltsville with a delegate living in the basement.")

The first thing Maloney learned after his election in November as one of the three delegates from the Laurel-based 21st district was that he had a lot of new friends. Interest groups that had considered him unworthy during his maverick-style election campaign suddenly were asking to have breakfast, lunch and dinner with him.

Maloney says the free meals sometimes looked tempting, since he had been without a paying job since last June, but says he declined most of the invitations.

"I was elected without any dues owed and I want to keep it that way for as long as possible," he said.

Maloney has some debts of another kind, however, such as the one to his car insurance company. But that will have to wait until Feb. 6, when he receives his first paycheck.

Malkus began drawing his paychecks from the legislature in 1947, after returning from World War II and winning his first term as a member of the House of Delegates. That was before the Bay Bridge was built, when lawmakers from the Eastern Shore took a ferry to the state capital and spent the night around the piano bar at Carvel Hall.

Those were the days when the Eastern Shore held the balance of power, electing nine of the Senate's 29 members, compared to one senator each from Montgomery and Prince George's counties. By the early 1960s, the state had passed its first reapportionment law and since then Malkus has watched "big spenders" and advocates of social change take control of the legislature.

Malkus' personal influence dwindled as he continued to lose battles against civil rights bills and new spending programs. By the late 1960s he was deposed as chairman of the Judiciary Committee after hiding an equal employment bill in his office safe to prevent it from reaching the Senate floor.

This morning, he awakened at 5:30, did a few chorses on his Dorchester County farm and set out for Annapolis. Once again he took the Senate floor to register his complaint that rural senators had been excluded from leadership positions in favor of representatives from the metropolitan area.

"There's one million people in the rural areas that are completely being ignored," he said, standing erect, his ample chest thrown forward. "If this continues you will create nothing but bitterness against the metropolitan areas that we had enough of after the Civil War. There's no reason why our country boys aren't given a chance."