Secret court orders authorizing electronic surveillance in foreign intelligence cases have increased almost 50 percent under the Reagan administration.

The continuing rise in the number of surveillance warrants issued by the federal Foreign Intelligence Surveillance Court was cited yesterday at an unprecedented public hearing on the workings of the 4-year-old panel.

"To date, the court has not rejected a single application," Mary C. Lawton, the Justice Department's counsel for intelligence policy, told a House Judiciary subcommittee for courts, civil liberties and the administration of justice. "We are proud of that record."

Last year the court approved 473 applications for electronic spy work, compared with 431 in 1981 and 319 in 1980, the last year of the Carter administration. Since the applications sometimes cover more than one technique or more than one target, the actual number of court orders was somewhat higher: 475 in 1982, 433 in 1981 and 322 in 1980.

Rep. Robert Kastenmeier (D-Wis.) said he convened the public oversight hearings, the first held since Congress passed the Foreign Intelligence Surveillance Act in 1978, in hopes of determining whether the legislation has had its intended effect of satisfying the needs of U.S. intelligence agencies while preventing abuses of constitutional rights in the name of national security.

There has been criticism of the court's usefulness because it has never denied a government application.

Lawton, whose office is in charge of making applications to the court, usually on behalf of the FBI or the National Security Agency, assured the subcommittee that it is "not a rubber-stamp court." She attributed the remarkable approval rate to the close scrutiny she said the applications receive beforehand, at both the intelligence agencies and the Justice Department.

A spokesman for the American Civil Liberties Union, attorney Mark Lynch, said, however, that there was no way of telling whether the law was working well or badly "because of the extraordinary secrecy" cloaking the court's operations.

The court is composed of seven jurists, currently headed by U.S. District Court Judge John Lewis Smith Jr., who rotate the duty of hearing applications for two days each month in a sixth floor conference room at the Justice Department.

Surveillance is supposed to be permitted only if there is "probable cause" to believe the target is a foreign power or an "agent of a foreign power."