CALCUTTA, Nov. 1—India's militarily explosive border with East Pakistan lies several hundred yards from the small frontier post of Boyra, where a smiling young Indian army lieutenant stood in ankle-deep mud Saturday afternoon gesturing toward the frontier.
"I will not be going with you," he told a half dozen foreign journalists, about to set off on foot across the frontier. "International law says we must not cross the border."
The officer repeated this stilted comment several times for the correspondents he had escorted through Indian army lines to Boyra. He evidently had eagerly rehearsed his words, which mirror all India's sensitivity now to events in Pakistan's divided eastern wing, and India's disputed role in them.
Boyra adjoins a section of guerrilla-held East Pakistan—which is called Bangla Desh by the geurrillas, who appear to have close contact with the Indian border police and the large number of troops who have been moved into the fields between Boyra and the frontier in the past two weeks.
The Indian lieutenant passed the journalists on to a wizened man of perhaps 60 years of age, who wore a World War II-style soupbowl steel helmet and carried an old carbine.
The man proudly identified himself as "Mukti Bahini", as the guerrilla military arm is known in Bengali, and then set off at a brisk pace through a drenching rainstorm.
Floundering in the thick mud, the journalists followed him on a twisting four-mile hike through rice paddies and beside a border marker dividing India and East Pakistan.
At the end of the march was an abandoned schoolhouse, now identified by a banner as subsector headquarters for the "Liberation Forces of Bangla Desh."
Maj. Najmul Huda, a 33-year-old precisely spoken man who said he had been a captain in the Pakistani army, asserted that from the schoolhouse he controls an area of 150 square miles. He has a company of about 100 regular soldiers who defected to the rebel cause, and 7,000 villagers trained by his forces.
The guerrillas claim to have implanted such headquarters throughout East Pakistan and say they are intensifying an insurgency that will drive the regular Pakistani army from the territory. "I think it will take a year or so, if we can continue the progress we have made recently," Huda said. "I am more optimistic now than I would have thought possible at the beginning, when we started out with no system, no order, no proper planning."
It is impossible to judge on a quick hike in and out of the rebel zone the validity of such claims. But impartial analysts outside credit the guerrilla organization with having expanded within seven months from zero to a force of 80,000 to 100,000 men, a figure roughly equal to the number of regular Pakistani soldiers deployed against them.
These analysts feel that the Mukti Bahini may be developing from a rag-tag hurriedly thrown together force into something of an organization, with increasing capability to coordinate actions among units.
Authoritative reports circulating in the diplomatic community here also support Maj. Huda's assertion that the Mukti Bahini has "become more aggressive and effective within recent weeks."
In the past 20 days, rebel attacks concentrated on communications and logistics lines show a pattern of increasing sophistication in the guerrillas' arms supplies and training, according to these reports, which add to the speculation that India may have recently stepped up tactical support for the guerrillas.
The guerrillas have been aided by the dispersal of Pakistani troops around the frontier over the past two weeks as India and Pakistan have traded threats of all-out war and moved their armies gun barrel-to-gun barrel along the borders.

PAKISTANI RETALIATION

The guerrillas' success in the interior has apparently led to an increasing retaliation by Pakistani forces against Indian border areas suspected of harboring guerrilla forces. They daily report shellings of villages, and in a few cases Indian areas are said to have been strafed by Pakistani aircraft.
Boyra is in an area that was shelled last week, with no substantial damage being done. A small trading town of a few thousand residents, it has not been deserted by its population, despite the heavy threat of war.
`This is our place," one farmer said as he stood in front of his hut, "we must stay, or others would take our houses and lands."
Camped in the fields between his hut and the border are several hundred Indian soldiers. All indications are that Indian troops have not crossed into East Pakistan to help the guerrillas.
Whether they support them in other ways is a matter of bitter dispute. While the Indians deny that they do, Pakistan routinely refers to the guerrillas as Indian agents or puppets, and President Yahya Khan has threatened to go to war with India if the guerrillas mount an effective campaign in East Pakistan.
Maj. Huda denied that his men receive any arms or training from the Indians. He attributed what he described as a significant increase in the number of weapons available to his men in the past few weeks to the increased capture of rifles distributed by the Pakistan army to loyalist civilians.
But there are persistent reports that a major influx of new arms began coming into the Indian border areas about 10 days ago. According to one version, which cannot be confirmed, Indian arms deliveries to the guerrillas were stepped up after the Soviet Union assured India that it would replenish weapons supplies sent to the rebel forces.
Wounded guerrillas are sent across the border into India for medical care, and the villagers in his area receive relief food from Indian Red Cross and Oxfam, a charitable British organization, Maj. Huda said.
The guerrillas and the Indian military also undoubtedly exchange intelligence, observers feel. Official leaks in New Delhi to the Indian press, confirmed by reliable Indian sources here, show detailed knowledge on the Indian side of the positioning of Pakistani forces throughout the country.
Asserting that his forces keep two Pakistan battalions tied down in the border region, Huda said that in the last 10 days his troops had completely disrupted the key rail link from Jessore to Benapole, forcing the Pakistanis to use road transport to supply the battalion at Benapole.
He also described in convincing detail a raid 100 of his irregular troops had made on a microwave radio station at Bhatiapara, 80 miles from the border, in the first week in October.
He estimated that his troops were recording about 70 confirmed dead each month, while losing men at about one-fifth that rate.
Once a captain in Pakistan's service corps, Huda uses mock-ups to train his men to blow up bridges and other targets.

THREE GOALS

"We have three goals at this stage in our war. First, we must disrupt their lines of communications. Then we will keep them under harassment by day and night, so they don't have enough food or sleep. And we must inflict as many casualties as possible.
"And there is one other thing, too. We want to take revenge, for what has been done to millions of Bengalis who have been driven from the homes or slaughtered."
On a short patrol in the territory around his headquarters, one of Huda's platoons carried a heavy machine gun, an American-made rocket launcher, and two trench mortars, which they said they had captured from Pakistani forces. The guerrillas seemed familiar with the weapons.
Huda also pointed out that the Mukti Bahini had recently graduated its first officers, a group of 57 who had been trained at an undisclosed location for the past three months. He said most of them were university students.
The apparent growing cohesion within the Mukti Bahini, and the emergence of officers like Maj. Huda as de facto district administrators, are trends that are being carefully scrutinized by Westerners who deal with South Asia problems.
"Some of us assume that East Pakistan will in fact be an independent country at some point," said one Western diplomat. "We don't know if it will take six months or six years. But if it does happen, there will be a new generation of leaders to have been formed in the guerrilla battle, and it will be important to know who they are."