The White House confirmed yesterday that President Nixon sent a personal letter to Cambodian president Lon Nol pledging that the United States would "stand side by side" with the Cambodian government, which is currently facing renewed military offensive by the revolutionary Khmer Rouge.

The New York Times had reported that the January 28 letter said. "The United States remains fully determined to provide maximum possible assistance to your heroic self-defense and will continue to stand side by side with the republic in the future as in the past."

All United States military activity in Cambodia was ruled out by a Congressional decree which went into effect August 15, ending 160 consecutive days of American bombing.

The Khmer Rouge yesterday continued to escalate their current dry-season offensive, tightening their grip around a trapped Lon Nol force of about 700 men just north of Phnom Penh despite repeated helicopter strafings directed against them.

The Khmer Rouge, who have pressed hard against Phnom Penh in recent weeks, are reported to be massing in several of the approaches to the capital and have reportedly intensified their shelling attacks.

U.S. Aid

The U.S. government has budgeted $580 million in aid for the Cambodian government this year, most of it intended to equip the Lon Nol Army and keep its propeller driven warplanes aloft.

Although the Khmer Rouge have only an estimated 18,000 soldiers within 25 miles of the capital, compared to 50,000 Lon Nol troops, the revolutionaries are considered better fighters and have managed to keep the pressure on.

The Khmer Rouge are led by prince Norodom Sihanouk, the former Cambodian ruler who was deposed in a 1970 coup and presently lives in exile in Peking.

Sihanouk, formerly a fierce neutralists, opposed the Khmer Rouge during his nearly two decades in power, but he allied himself with them after he was outsted and he is presently viewed as their leader.

The Khmer Rouge, small and powerless during the Sihanouk years, grew in numbers dramatically after the Lon Nol takeover and the ensuing American bombing.

Initial reports claimed that they were North Vietnamese, but since then it has been widely acknowledged that they are indigenous Cambodian revolutionaries, receiving only material aid and training assistance only material aid and training assistance from North Vietnam.

The Khmer Rouge is now estimated to number at least 200,000.