Because of an editing error, an article on page A21 yesterday incorrectly said the Pentagon had acknowledged that sending two U.S. warships within six miles of the Soviet Black Sea coast was "clearly provocative." It should have read: "The Pentagon acknowledged the presence of the warships in responding to a formal Soviet protest that the action was 'clearly provocative.' "

The Soviet Union today protested what it called a "defiant" and "provocative" violation of its territorial waters by two U.S. warships last week and it warned that repetitions could lead to "serious consequences."

The sharp protest of the Thursday incident in the Black Sea appeared to be a further setback in relations between the two countries, which have been strained in recent weeks by expulsion orders, accusations of espionage and exchanges of criticism.

In discussing the latest protest at a press briefing today, Soviet Foreign Ministry spokesman Vladimir Lomeiko also accused President Reagan of putting new obstacles in the way of improved relations and gave no indication of progress toward setting a date for a tentatively planned summit meeting between the U.S. and Soviet leaders in Washington later this year.

The confrontational approach today indicated, observers said, that the Soviets are willing to take a hard line as they prepare for the proposed summit between Reagan and Soviet leader Mikhail Gorbachev. Tentative agreement to the meeting was one of the chief accomplishments of the two leaders' talks at Geneva last November.

The protest was seen here as further Soviet reaction to a recent U.S. order that the Soviet Union reduce the size of its staff at the United Nations, a move Washington linked to charges of "wrongful acts" by the Soviets, including espionage. Four days ago the Soviets accused a U.S. diplomat here of spying and ordered him out of the country.

Today's Soviet note, delivered to the U.S. Embassy, charged that two U.S. Navy vessels, the cruiser Yorktown and the destroyer Caron, penetrated six miles inside the Soviet Union's 12-mile territorial limit along the southern Crimean coast on Thursday and remained there two hours.

According to the official news agency, the note charged that the incident was "of a demonstrative, defiant nature and pursued clearly for provocative aims." Tass added that it was not the first time that U.S. naval ships "deliberately" violated Soviet territorial limits, and it said the note warned that such violations can have "serious consequences" for which the United States would be wholly responsible.

[The Pentagon acknowledged Tuesday that the action was "clearly provocative," Washington Post staff writer George C. Wilson reported. But it said that the ships, which were following orders approved by the White House and the State Department, were simply exercising "the right of innocent passage."]

["International law has long recognized the right of ships of all nations to engage in innocent passage through a country's territorial seas without prior notification to, or permission of, that country," it added.]

According to diplomats here, there have been disputes over whether the border of the 12-mile zone duplicates the ragged coastline of the Black Sea, which is bordered by the Soviet Union, Turkey, Romania and Bulgaria. Most of the Black Sea is international water.

A U.S. Embassy spokesman confirmed delivery of the protest note but would not discuss its contents.

The embassy also has refused to comment on the order to expel Michael Sellars, a second secretary accused by Tass on Friday of holding a clandestine meeting with a Soviet citizen for the purpose of gathering intelligence.

At today's press briefing, Lomeiko repeated the Soviet position that the next summit meeting should be "productive," and not held "just for the sake of a meeting."

Gorbachev, speaking last month to the Communist Party congress, linked the holding of a summit meeting to progress on two areas of arms control: a joint ban on nuclear testing and elimination of U.S and Soviet missiles in Europe.

Soviet spokesmen denied that Gorbachev had set conditions for the summit, but western diplomats here saw the linkage as an attempt to focus public pressure on those two issues. Lomeiko said today that the Soviets would make their proposal on the timing of the summit "as soon as conditions are ripe."

Lomeiko accused Washington of taking a "negative approach" to Gorbachev's latest proposal to extend a unilateral Soviet moratorium on testing. He also accused Reagan of raising the world's trouble spots -- including Nicaragua -- as obstacles for improved relations with the Soviet Union.

Referring to Reagan's recent message to Congress on "regional issues," Lomeiko said he had "resorted to anti-Soviet invectives in a bid to mask the policy of state terrorism."