The United States denied yesterday that it has encouraged Somali to back guerrillas fighting to wrest the Ogaden desert from Ethiopian rule.

The denial was in response to a report in Newsweek that the Somalis felt that the United States misled them in June about supplying military aid, an offer they claim led them to invade the Ogaden region the next month.

Tom Reston, deputy assistant secretary of state for public affairs, said at a briefing, "I can categorically deny the implication that the United States encouraged in any way Somalia's support for the escalated fighting in the Ogaden."

Reston added that the U.S. arms offer came "when Somalis told us of their desire to have an alternative to total reliance on Soviet arms." At the time the Soviet Union was shifting its support to Somalia's longtime rival, Ethiopia, and President Carter was saying he was inclined "to aggressively challenge, in a peaceful way, of course, the Soviet Union and others for influence in areas of the world that we feel are crucial to us now or potentially crucial."

In June, according to Newsweek, Somali President Mohammed Siad Barre sent his American physician and adviser, Dr. Kevin Cahill, to confer with State Department counselor Matthew Nimetz. Cahill reported that top U.S. officials were "not averse to further guerrilla pressure in the Ogaden," Newsweek said.

It added that Somalia's ambassador to Washington conferred twice with Carter and assured Siad Barre that Cahill's message was accurate.

Reston said the Somalis had misinterpreted U.S. comments during the June meeting. "U.S. officials insited that any military supplies we might provide would be for defensive purposes only," he said.

The Somalis were told that the equipment was meant "to fill any gaps which might exist or might develop in Somalia's ability to defend its internationally recognized territory," Reston said.

The State Department also said it had no plans to resume the arms shipments to Ethiopia that it had canceled April 23. But Reston said U.S. embassy officials have recently met with Ethiopia's military strongman, Lt. Col. Mengistu Haile Mariam, to discuss U.S.-Ethiopian relations, including economic assistance.

News agencies reported the following:

Informed sources in Addis Ababa, Ethiopia's capital, said bombing raids went on throughout the day against Somali tanks, guns and infantry. Ethiopian pilots, according to the reports, downed 28 Somali Migs.

In Mogadishu, Somali, a rebel spokesman said an advance party of rebel forces was on the outskirts of Harar, one of Ethiopia's last two strongholds in the Ogaden. Jigjiga, an Ethiopian tank and radar base, was captured by rebels forces week, according to reports in Mogadishu. Dire Dawa, another stronghold, remains in Ethiopian hands.

Reports from rebels in Mogadishu said that the main attacking force of the Somali-backed guerrillas was six miles from Marda Pass4, the historic route leading to Harar, Dire Dawa and then into the Ethiopian heartland.