From the federal courthouses in Baltimore, Richmond and Washington to the marble-halled agencies of the Federal Triangle, the election of Republican Ronald Reagan as president and a Republican-controlled U.S. Senate will dramatically reshape the Washington area's political and judicial landscape.

The new Republican administration will most profoundly affect the District, where voter-approved petitions for statehood and gambling, along with hopes for expanded home rule and a fixed federal payment, are likely to face strong opposition, as will a pending nomination of the city's first Latino judge.

In Maryland, Sen. Charles McC. Mathias, given an overwhelming mandate by the same voters who rejected Reagan's candidacy, has emerged as a powerful member of what suddenly is the majority party in the Senate.

But the liberal Mathias, who is in line to become chairman of both Senate subcommittees that oversee District affairs, served notice yesterday that he is no more likely to give the District a free hand in deciding its own fate than has a generation of Democratic predecessors. Although Mathias insists he is committed to full home rule for the city, he said he will oppose any effort at statehood; believes the annual federal payment should be arrived at through negotiation between Congress and the city government, and doesn't believe the proposed lottery is a good way for the city to attack its financial problems.

In Virginia, two newly elected Republican congressmen, Stanford E. Parris and Frank Wolf, are unlikely to vote much differently on such local issues as Metro funding, opposition to a commuter tax reduction of flights at National Airport, than the two Democrats they replaced in Northern Virginia's 8th and 10th Congressional Districts. But first-term GOP Sen. John W. Warner will continue his ascent to power, overnight qualifying both as a subcommittee chairman and the direct link between the White House and patronage appointments in Virginia.

The effects of the Republican era are already being felt in the federal work force of this area. The first of an estimated 20,000 political appointees whose jobs are on the line got blue slips yesterday. About one-third of the employes of the Senate Judiciary Committee, whose chairmanship will be transferred from the office of Sen. Edward M. Kennedy (D-Mass.) to Sen. Strom Thurmond (R-S.C.), were notified yesterday that their employment would cease at the end of the year.

Other imminent transformations as the result of the transition of power will include new U.S. attorneys for the District, Maryland and Virginia, and the coup de grace for the nomination of a black federal judge of Virginia. a

A close supporter of Richmond Circuit Court Judge James E. Sheffield's appointment to the federal bench, State Del. Benjamin Lambert (D-Richmond), said yesterday, "It's all over for Sheffield."

Lambert based his assessment on the defeat of Northern Virginia Rep. Herbert E. Harris II by Parris. Lambert said Harris was Sheffield's key to another hearing before the Senate Judiciary Committee. Sheffield's initial nomination hearing was delayed last summer at his own request, to give him time to study Internal Revenue Service files on his income-tax records that his opponents had produced in an effort to block his confirmation.

Even without Harris' defeat and Reagan's election, President Carter's effort to make Sheffield the first black federal judge in Virginia history had been imperiled by the strong opposition of Virginia's independent Sen. Harry F. Byrd Jr. The combination of those factors makes the Sheffield nomination "a dead issue," Lambert said.

Byrd, the only independent in the Senate, ended speculation yesterday that he might switch allegiance and vote with Republicans to organize the Senate. Even though he endorsed Reagan, Byrd said, "I expect to vote as I have in the past, namely, with the Democrats on procedural matters and independent of party lines on legislation."

While Thurmond will be the new chairman of the Judiciary Committee, it might well have been Mathias, had not Thurmond decided two years ago to give up his spot on the Armed Services Committee for Judiciary. Because of his greater seniority, Thurmond's "end run" moved the elderly, conservative southerner in front of the liberal Mathias as the ranking Republican on the powerful committee.

Three other judicial nominees in the region are expected to be lost in the scramble by Democrats to enact more sweeping legislation in the closing days of the 96th Congress, which begins a lame duck session next week.

Ricardo M. Urbina, 34, a law professor at Howard University, and Dorothy Sellers, 37, a District lawyer, were nominated by President Carter in September to fill the vacancies on the D.C. Superior Court. And in Virginia, the nomination of Abingdon lawyer James Jones, withheld in the face of a filibuster threat by Thurmond last month, become another casualty of the change in administrations.

While both Parris and Wolf said they generally agree with positions on vital local issues that were staked out by Harris and Fisher, neither of the new Republican House members from Northern Virginia expressed an interest in serving on the House District Committee, of which Harris had been a subcommittee chairman and active member.

During the campaign, Harris criticized Parris for refusing to commit himself to membership on either the District or Post Office and Civil Service committees, the two assignments in the House that most often affect area residents. A spokesman for Parris said yesterday that "we know of no local issue" on which Parris differed from Harris' position. But an aide to Harris insisted that it is not enough to vote correctly, but "it's a matter of how much time you devote to working for those issues. That's the way you get legislation passed."