The United States expressed heightened concern yesterday about the border war between North and South Yemen as Saudi Arabia canceled all military leaves and arranged for an emergency meeting of the Arab League to try to stop the fighting.

State Department spokesman Hodding Carter, while backing the Saudi effort to obtain a negotiated solution, also announced that the United States is speeding delivery of $100 million in weapons to North Yemen, where the United States recently displaced the Soviet Union as chief arms supplier.

The United States also has discussed the fighting with the Soviets, who are the main suppliers and advisers to South Yemen, Carter said. He gave no details of the diplomatic approach or its results.

For the Saudis, who prefer backroom diplomacy, the cancellation of leaves and suggestion of military action is a sharp departure from their usual low-key approach to reginal issues. They are particularly sensitive to developments in the rival Yemen states, both of which are on the Saudi border.

Saudi Arabia already has said that the Yemen conflict threatens its security and that of the entire Arabian Peninsula. The Saudi announcement that all military personnel should return to their duty stations did not specifically mention Yemen but ascribed the action to "prevailing circumstances."

The U.S. response clearly was triggered by the Saudi concern. In the second statement this week on the subject of the Yemen border war, spokesman Carter called for hostilities to cease, occupying forces to with-draw and all parties to support the principle of nonaggression.

He said the United States has "indications" that forces from South Yemen have crossed the border and occupied some positions in North Yemen. He said the U.S. "national interest" in the security and integrity of the Arabian Peninsula is involved in the fighting.

Carter said the weapons deliveries to be speeded included light antitank weapons, recoilless rifles and antiaircraft guns. He noted that the State Department had notified Congress on Monday that about $400 million more in arms sales are planned for North Yemen, including 12 F5E fighters, 100 armored personnel carriers, 64 M60 tanks and two C130 transport aircraft. All the weapons are to be financed by Saudi Arabia.

The Saudi news agency quoted Prince Saud, the kingdom's foreign minister, as emphasizing the need for a speedy Arab League meeting to discuss "the deteriorating situation" in the Yemens. Arab league Secretary General Mahmoud Riad announced that a ministerial level meeting will be held on the issue Sunday in Kuwait.

The border war matches South Yemen, the only Marxist Arab state, against moderate, pro-Western North Yemen, but its roots go back deep in time and tribal rivalry. Fighting has increased in the past week, during which South Yemen reportedly has captured three border towns from the North.

The Saudi newspaper Al Nadwa reported that the Saudis also are calling home the 4,500-man contingent of troops stationed in Lebanon with the Arab peacekeeping force. There was no independent confirmation of these reports, but if true they would have two significant consequences.

One is that the peacekeeping force in Lebanon, set up on Saudi Arabia's initiative in 1976, would lose most of what remains of its veneer of internationalism, since it already is a virtual occupation force of the Syrian Army. The other is that it would return to Saudi Arabia the few troops in the 62,000-man armed forces who have ever seen a shot fired in anger.

Diplomats with experience in Saudi Arabia and the Yemens said, however, that it was highly unlikely that Saudi Arabia would risk direct military intervention in the Yemen war.

The Saudis are known to be hostile to South Yemen, with its close ties to the Soviet Union and its radical internal policies, but they have recently renewed diplomatic contacts. South Yemen's foreign minister, Mohammed Saleh Moutih, has visited Riyadh twice in the past week.