President Reagan is expected to nominate Laurence H. Silberman, a former deputy attorney general and one-time ambassador to Yugoslavia, to a vacancy on the influential U.S. Court of Appeals here, according to informed sources.

The sources said two other Washington lawyers -- Marion E. Harrison and Philip A. Lacovara -- are under consideration by a high-level White House selection committee for a second opening on the appeals court, although Harrison is considered the leading contender.

During his first term, Reagan appointed three conservative Republicans to the court, which has been dominated by a liberal majority since the early 1960s. A 12th seat created last year by Congress is one of the positions to be filled.

The other vacancy occurred last month when Judge Malcolm R. Wilkey entered semiretired, senior status.

Sources also said this week that Alex Kozinski, chief judge of the U.S. Claims Court here since 1982, is expected to be nominated to fill a vacancy on the 9th U.S. Circuit Court of Appeals in California.

If confirmed, Kozinski, 34, a self-described "loyal Reaganite," would be the youngest sitting federal appellate judge since William Howard Taft was named to the bench in 1892, also at age 34.

The selection committee also is said to be prepared to pick Loren A. Smith, 40, chairman of the Admin-istrative Conference of the United States, for nomination by Reagan to the Claims Court. An aide to Smith confirmed yesterday that Smith is under White House consideration.

The court hears claims for money against the United States, including tax refund matters and contract and patent disputes.

Judges on the Court of Appeals are paid $80,400 annually, while those on the Claims Court are paid $67,800 a year.

Smith, chief lawyer for Reagan's 1980 campaign and a senior Reagan transition official, formerly taught constitutional law at the Delaware Law School of Widener College. He was unavailable for comment yesterday.

Silberman, 49, served as solicitor in the Labor Department in 1969 and 1970, when he was promoted to undersecretary. He was deputy attorney general under William Saxbe during the final six months of the Nixon administration.

Shortly before President Nixon's resignation, Silberman resisted a presidential attempt to halt the prosecution of a Nixon friend and former Cabinet member, John B. Connally. The move was abandoned after Silberman threatened to resign.

Silberman was named ambassador to Yugoslavia in 1975 by President Ford and served two years. He was a controversial envoy with a blunt-spoken, no-nonsense style.

Criticized once in a letter from a supporter of Yugoslav President Tito, Silberman replied: "I have received your letter of Aug. 4th. Kiss my ass. Sincerely." Silberman was introduced by Saxbe to the Justice Department staff as "meaner than a junkyard dog."

Silberman, a partner in the Washington office of a San Francisco-based law firm, Morrison and Foester, declined to comment yesterday.

Kozinski was born in Bucharest and came to the United States in 1962. A 1975 UCLA law graduate and former clerk for Chief Justice Warren E. Burger, he worked briefly as a lawyer in the Reagan White House before being named special counsel to the Merit Systems Protection Board in 1981.

In that post he drew the ire of Rep. Patricia Schroeder (D-Colo.) and others who accused him of being unsympathetic to federal workers and who urged that the position be abolished.

Kozinski declined to comment yesterday on his possible judicial selection.

Harrison, 53, a partner in the Washington firm of Scott, Harrison and McLeod and a Republican candidate for the Virginia House of Delegates in Arlington in the early 1960s, said he had heard informally that he is under consideration for the appeals court but he could not comment further.

Lacovara, 41, former counsel to the special Watergate prosecutor and now a partner in Hughes, Hubbard and Reed here, was abroad yesterday and was unavailable for comment.