D.C. Superior Court Judge John Garrett Penn, who is highly regarded in Washington's legal community for his common sense approach to deciding cases and his even-handed judicial temperament, has emerged as one of the leading candidates to fill a vacancy on the U.S. District Court here.

While Penn, other Superior Court judges and numerous city lawyers are under consideration by the D.C. Judicial Nominating Commission for the seat left vacant by the death of Judge Joseph C. Waddy, the names of 40 applicants have already been submitted to the commission for nomination to two new seats on the U.S. Court of Appeals here.

The unusual occurrence of three simultaneous federal court vacancies here forcuses attention on the previously little-known commission headed by former Maryland senator Joseph D. Tydings and at the same time has led to discreet lobbying within the legal community for specific candidates for the lifetime appointments.

Anyone can submit a nomination to the 11-member commission and the panel has been screening 76 names in an effect to winnow the list to five nominees for the Waddy seat. The names of the five possible nominees will be submitted to the White House on Monday, according to one source close to the commission, and then, after Justice Department background checks on the contenders, President Carter will submit one name to the Senate for confirmation.

The D.C. commission is one example of Carter's nationwide effort to take the selection of federal judges out of politics and place it on a merit basis. As a result of a judeship bill passed recently by Congress, 117 new District Court judges will be selected and 35 new appellate judges.

For years, senators of the same political party as the White House incumbent have sent the president the names of their federal judicial choices and presidents have more of less routinely submitted the names to the Senate for confirmation.

During his 1976 campaign, Carter promised to name federal judges on a merit basis and, according to the American Judicature Society, a group that studies and promotes court reforms, has been somewhat successful.

However, when powerful senators objected to establishing judicial nominating commissions to pick district court judges, Carter compromised and agreed to establish the commissions only for appeal court nominations. But there are no senator in the District of Columbia and so the Tydings group nominate judges for both courts.

Larry Berkson, an official with the Judicature Society, gave the D.C. commission high marks for its elaborate screening process of the judicial candidates. He said that senatorial-appointed commissions in 17 states, including Virginia, have made some good choices and some that have been lacking.

The D.C. commission, according to the source familiar with its operation, requires that any of the 11 members on the panel must report any comment made to them about prospective nominees. While there apparently has not been a great deal of lobbying of the panelists, the source said that at one time or another D.C. Walter E. Fauntroy, Mayer Walter E. Washington and City Council Chairman Sterling Tucker all have written recommendations on behalf of judicial candidates.

The judicial candidates here are required to fill out extensive questionnaires about themselves and list the names of 10 attorneys who have oppoed them in court cases, if they are lawyers, or appeared before them, if they already are lower court judges. In addition, lawyers are required to list the five most important cases they have worked on and judges list the five most important opinions they have written.

Carter has nominated three people for the U.S. District Court bench here, all of them from lists submitted by the Carter' appointed commission. Two of them, Louis F. Oberdorfer and Harold Greene, are now judges, but the nomination of the third, Carin A. Clauss, has run into difficulty and is still awaiting confirmation.

Penn has twice been passed by when Carter picked the three other nominees in the last year for the federal bench. But a variety of Washington judges and lawyers say that the 46-year-old Superior Court Judge, is, for several reasons, a good bet to be selected this time.

If nominated by Carter and confirmed by the Senate, Penn would become the fourth black among the 15 full-time federal District Court judges in Washington.

But before Penn, a Superior Court judge since 1970, can be nominated by the president, he must again survive the D.C. Commission's screening process. Penn's chief attributes are that he is praised by numerous people who have had dealings with his court and the fact that he is black, as was Waddy.

"Judge Penn is careful, thoughtful and has good judicial temperament," said one lawyer familiar with Penn's performance.

At the same time, however, the lawyer said that a black is almost certain to get the Waddy seat. He also said it is likely that the names of most, if not all is black Superior Court Judges are among the 76 possible contenders.

Three other Superior Court judges are reportedly also possible contenders for the Waddy seat, including Norma Johnson, who is black, and two white judges, Joyce Hens Green and Syivia Bacon.

Penn presided over two significant city tax cases last year, unpholding the legality of a controversial tax on professionals who work in the District in one case and then later ordering the city to return as much as $7 million from the tax receipts on professionals because some people had to pay it sooner than others.

Several legal sources in Washington said theat Carter is likely to name at least one woman to the appeals court. There currently is only one woman on a federal appeals court, Shirley M. Hufstedler, who serve on the 9th Circuit Court of Appeals on the West Coast.

One possible nominees for the appeals court is patricia Wald, the Carter administration's 50-year-old assistant attorney general for legislative affairs, according to various legal sources. Until joining the Justice Department last year, she had been director of litigation for the Mental Health Law Project and once served as the co-director of the Ford Foundation's drug abuse project.

Besides Tydings, there are six other lawyers on the nominating commission, Wesley Williams, Robert Watkins, Michael Gottesman, Erwin Griswold, Marna Tucker and Patricia King. The other members of the commission are John Jacob, executive director of the Washington Urban League; Julia Walsh, who heads her own investment firm; Floretta McKenzie, a deputy superintendent of the Montgomery County school system but a D.C. resident, and Lorraine Williams, Howard University's vice president for academic affairs.