CHIANGMAI--Though the United States' military muscle in Thailand is concentrated in the dry northeastern plateau, bits and pieces of the war effort have spread into the mountains and plains of the North. At present the United States has three major electronic stations in this region and appears to be building a fourth. The Central Intelligence Agency (CIA) is present in force as well.

CIA operations in the North are headquartered here in Chiangmai, Thailand's second largest city. Reportedly housed in a two-story, antennae-studded building in the American consulate compound, agents work with the Thai Army, the paramilitary Border Patrol Police, and other Thai and American contacts to keep tab on the North's sometimes rebellious hill tribes, Burmese rebels operating out of Thailand, and "unfriendly" forces in Laos.

According to a foreign journalist living in this city, the CIA 18 months ago had 142 persons on its payroll, including 38 Americans. He sees no reason to think the number has declined since then.

Out at Chiangmai Airport is a terminal and warehouse for the CIA's transport contractor, Air America. A short take off and landing plane is usually in sight there.

Members of the US Army, Air Force and Coast Guard are stationed in Chiangmai and Lampang, the neighboring province to the south. They help man a radio-telephone relay station, an aerial navigation radio beacon transmitter, and a secrecy-shrouded satellite tracking station.

Several miles south of Lampang's provincial capital is the tracking station, designated Koka after a small town nearby. It is the home of approximately 250 Americans and is a self-contained community. It features, among other things, a Non-Commissioned Officers' Club, a baseball diamond, and instruction in Korean Karate.

Large-diameter radar dishes that oscillate rapidly stand out among the drab one-story buildings and chainlinked fencing. Americans working at Koka are even more tight-lipped than usual in answering queries about the base's functions. The same is true of Bangkok officials.

"It's not our policy to comment on the internal operations of American installations," replied the American Embassy spokesman in reply to a series of questions about Koka.

General Electric reportedly employs about 40 American civilians at top salaries to service the tracking equipment. An American company called Trans Asia operates the power plant. Because security at Koka is high, information about additional functions must be confined to speculation.

Theories run that computers at Koka command radar-automated bombing along the Ho Chi Minh trail. In this top secret weapons system a master computer sets a bomber's course and releases the plane's ordinance automatically to hit a set of radar coordinates.

Other observers think it might be an eavesdropping post for Chinese and Burmese radio messages. Still others think the base might be part of an early warning system in the event of attacks against Thailand by enemy aircraft.

Just north of the provincial capital of Lampang is one of four LORAN-C stations, acrial navigation transmitters, that the US Coast Guard operates in Southeast Asia. By taking fixes on the beams of three of these stations, American aircraft in flight can determine their exact positions.

The station, manned by approximately 30 Coast Guardsmen is used primarily to direct B-52s flying from Thailand, according to sources in Chiangmai.

The other three LORAN stations are located in U-Tapao, Thailand, (home base for the B-52 force here) on a South Vietnamese prison camp island off the southern tip of South Vietnam, and near Hue, South Vietnam, close to the Demilitarized Zone.

At Chiangmai Airport the US Army maintains a telephone relay station which consists of two olive drab receiving-transmitting dishes and a number of trailers and support vehicles. There are approximately tea of these stations throughout Thailand and they make possible a military-police telephone system.