By charging that the United States financed a "colossal" conspiracy to overthrow him, Prime Minister Zulfiqar Ali Bhutto attempted - apparently successfully - to trap Pakistan's armed forces into his struggle for political survival.

The ploy weakened Pakistan's warm relationship with the United States, but from Bhutto's viewpoint the loss is relatively marginal and temporary. The support of the half million-strong armed services is of far greater concern and more immediate party Pakistan National Alliance (PNA) trying to force him from office.

Bhutto's accusation made in a parliamentary address April 28 and since then magnified daily by Pakistan's controlled news media, forced the military to come to the aid of the country and its leader against an alleged threat by the United States.

To do less would have made the patriotism of the armed forces, especially the 400,000-member army, suspect in the eyes of many Pakistanis. This nation, like its neighbor, India, has long been a hothouse in which the seeds of conspiracy flourish.

Certainly not all 74 million Pakistanis believe Bhutto's charges against the United States. Some say they consider them false, but doubt has been planted in enough minds to halt the erosion of popular support for the Prime Minister.

If any doubt remained about the armed forces position after the joint Chiefs of Staff pledged their allegiance to Bhutto after his speech: it was eliminated Friday in Lahore when soldiers killed three men taking part in a noisy but peaceful demonstration against Bhutto.

The soldiers and their victims were all Punjabis. Punjab, with its 40 million people, is the most populous of Pakistan's four provinces. Punjabis comprise 65 per cent of the army, and Lahore, the administrative and cultural capital of Punjab, has historically been the fulcrum of Pakistani politics.

These latest three killings, in two months of violence that has taken some 300 lives, could readily be explained as the hasty misjudment of a young and jittery officer. But they are seen in Lahore as irrefutable evidence that Punjabi soldiers are prepared to kill Punjabi civilians to maintain Bhutto's leadership.

Thus, whether the army's leaders sincerely believe that the United States was plotting to overthrow the Prime Minister or not, they have bound themselves and their troops to Bhutto - in writing and now in blood.

There are, without doubt, strains within the army. One brigadier general in Punjab is under investigation for a letter he wrote to his commanding officer, complaining that the army was being "misused" in a political battle. There are also unconfirmed reports that seven junior officers are being held for courts-martial in Karachi.

So far, however, the strains have not broadened into serious, discernible splits. The army seems essentially unanimous in its commitment to its top officers and, in turn, to Bhutto. Although the opposition Alliance's most popular leader is retired Air Marshal Asghar Khan, an appealing figure with exploitable military connections, the army for now seems more comfortable with Bhutto.

The opposition seems muddled in its thinking on how to deal with the army. Asghar Khan, an appealing figure with exploitable military connections, the army for now seems more comfortable with Bhutto.

The opposition seems muddle in its thinking on how to deal with the army. Asghar has appealed to officers to disobey "illegal orders" from Bhutto. His colleagues have said that they do not want to force a confrontation with the military because they are counting on the army to insure fair elections, if Bhutto accedes to the demands to restage the March 7 polling the opposition claims was rigged.

But Friday's incident in Lahore, whatever its original intention, has certainly driven a sharp wedge between opposition followers at least in Punjab, and the military. And by arresting virtually every opposition leader of significance. Bhutto has managed to keep leaders and followers from meshing their plans and actions.

Because the military question is so vital and senitive, it is left out of local newspapers and broadcasts. Instead, the media are conducting a campaign of broad anti-American charges based on the issues Bhutto stressed in his speech.

These are that the United States poured millions of dollars into Pakistan to fund the opposition and that Washington wanted Bhutto out of the way because he:

Would not bow to U.S. pressure to halt a deal with France to built a nuclear reprocessing plant in Pakistan:

Had opposed U.S. involvement in Vietnam:

Was too vitriolic in his commitment to the Arab cause against Israel:

Was too vitriolic in his commit-independence-mined a leader of the World.

Non-American diplomats in the Pakistani capital Islamabad, consider all but the reprocessing plants issue red herrings. Assessments of the seriousness of the nuclear issue are mixed.

Some have concluded that the Carter administration's commitment to halt nuclear proliferation might have induced the Central Intelliegence Agency to support Bhutto's opposition.

But these diplomats say they have no specific proof. One West European confirmed Bhutto's claim that an influx of dollars had forced the black market exchange rate for the Pakistani rupee down. But he also said that a relatively small amount, as little as few hundred thousand dollars, could have this effect, and that such an amount could have been set free be overseas Pakistanis opposed to Bhutto.

An Asian envoy said the U.S. Embassy had shown an "excessive academic interest" in the election campaign. But he readly allowed that this was in no way proof of any untoward involvement.

One specific occurence that some observers believe indicates a measure of U.S. intentions was the Carter administration's withdrawal of George S. Vest as its nominee for ambassador to Pakistan. Although Vest has reportedly been replaced for Arthur Hummel, currently Assistant Secretary of State for East Asia and Pacific Affairs, some observers believe the move was more than a signal of Washington's displeasure.

A European diplomat noted that Vest was a practiced negotiator in nuclear affairs and that his assignment was intended to put someone in Islamabad who could talk Bhutto out of the processing plant or submit the French guarantees to greater safeguards. As a fluent French-speaker. Vest was also supposed to be able to deal with the French embassy, the diplomat said.

Now that Bhutto has made U.S. opposition to the plant a major public issues, the envoy reasoned, sending Vest to Islamabad would be "too obvious."

Other observers, who ware considerable more eynical about a U.S. conspiracy. note that Bhutto was in no way cornered by Washington's pressure against him and France to halt the project.

For one thing, initial construction work on the project, located near Chashma, a Punjab town on the Indus river, began six months ago. And although the present $200-million cost of the plant is expected to rise markedly during the 19 years before it is operable. France has shown no sign of changing it mind."

In essence, Bhutto appears to have decided that, with his future in real jeopardy and the backing of the Army a vital requirement for survival, he would have to lump together whatever issues he could expect to produce positive reaction in the military and civilian populations.