Amid warnings of military strikes, President Clinton said Friday the United States and its allies must remain "very, very strong" in demanding that Yugoslav President Slobodan Milosevic loosen his stranglehold on ethnic Albanians in Kosovo.

"I believe our allies in Europe are with us," the president said. "I think we all understand, and I hope he got the message." Secretary of State Madeleine Albright and Defense Secretary William Cohen told lawmakers that NATO is poised to strike Serb targets if last-ditch diplomatic efforts fail."We need to stop the violence, get a negotiated settlement and work our way through this," Clinton said, stopping to talk with reporters on the South Lawn before boarding a helicopter for a trip to Ohio and Pennsylvania. "We don't want thousands upon thousands of people to be caught up in a war or to starve or freeze this winter because they have been displaced.

"We cannot allow this conflict to spread again and risk what we stopped in Bosnia starting over again in Kosovo," Clinton added. He said he was "quite hopeful we'll have a positive resolution of it."

Albright, after a 21/2-hour closed-door briefing for senators, said, "We have consistently been working to get NATO ready, and NATO is now prepared to act." Still, she said, "We believe that the best solution continues to be a diplomatic solution."

In Pristina Friday, Yugoslavia's Serb leadership invited U.N. chief Kofi Annan to visit, saying it would help him understand "the real situation in Kosovo" after international condemnation of massacres of ethnic Albanian civilians and the threat of NATO airstrikes.

But in New York, Annan's spokesman, Fred Eckhard, said the secretary-general declined, saying he was already receiving reports from U.N. officials in the area.

The invitation, carried by the state-run Tanjug news agency, came after an ethnic Albanian man gave human-rights workers a graphic account of what he said was a massacre of 13 ethnic Albanian men by Serbian police in a Kosovo forest on Saturday.

The Serb invitation also came days before Annan is scheduled to submit a report on compliance with a U.N. Security Council resolution demanding an end to the Kosovo offensive by Serbian police and the Yugoslav army. The resolution threatens unspecified further action if the demand is ignored.

Serb police have denied killing civilians, and Yugoslav Foreign Minister Zivadin Jovanovic said Thursday in Washington that his government is willing to let an international team take part in an investigation to "establish and prove the facts."

In New York, the U.N. Security Council condemned "those responsible" for the bloodletting in Kosovo, but Britain and the United States failed to convince Russia and China to specifically blame the Serbs. The council called on Milosevic to identify, find and punish the killers.

"This is a humanitarian disaster," Prime Minister Tony Blair told Channel 4 TV News in London. "I believe it will only be stopped if Milosevic gets the clearest possible message, namely, if you carry on doing this, you will face a military penalty."

But Russia's parliament declared Friday that any NATO military action taken without U.N. approval would be considered an "illegal act of aggression."

Albright said suffering of refugee ethnic Albanians was an uppermost concern.

"We are very concerned about the humanitarian situation and are working with various agencies to try to get some relief for the people that are up in the hills there," she said.

Cohen said Milosevic must pull back his army and police in Kosovo, must allow the movement of humanitarian aid, must "allow displaced persons to return to their homes, and then sit down and seek a diplomatic solution to the conflict."

Nine out of 10 people living in Kosovo are ethnic Albanians. Hundreds have been killed since Serbs began cracking down on Albanian separatists in the province in February.

"There is an `atrocity threshold' right now," Sen. Kay Bailey Hutchison, R-Texas, said after Thursday's briefing. "The world is not going to stand by and watch people murdered."

The State Department issued a travel warning Thursday urging Americans not to visit Yugoslavia and for Americans now there to consider leaving.