The Office of Management and Budget has proposed phasing out the familiar Head Start program for preschool children from low-income homes by merging it into a community services block grant, sources said yesterday.

Head Start was one of the social "safety net" programs the Reagan administration called inviolate earlier this year.

The OMB plan to eliminate its separate identity and shift its funds to the block grant over four years has been sharply protested by Health and Human Services Secretary Richard S. Schweiker in a letter of appeal to OMB Director David A. Stockman, sources said.

Schweiker, fighting several fiscal 1983 cuts proposed by Stockman, reportedly said in the letter that he opposed putting Head Start into a block grant.

Equally important, Schweiker told Stockman, under the OMB plan total funding available for Head Start in fiscal 1983 would be $780 million, substantially less than the $950 million the president originally proposed for 1982 and the $912 million for fiscal 1982 that Congress has provided in the latest government funding resolution.

Schweiker, objecting strongly to the funds reduction, said, "I believe the president appropriately placed Head Start as one of the 'safety net' programs."

In the same letter, sources said Schweiker warned Stockman that other OMB-proposed 1983 cuts would undermine medical research in the United States, block further progress in disease control and violate treaty obligations to American Indians.

Calling such cuts "unwise and inappropriate," he also said that Stockman's proposed one-third personnel cut in the HHS division that manages Medicare and Medicaid programs would make it extremely difficult to maintain control over these two programs, among the largest and fastest growing in the government. He also objected to elimination of funds for a separate office on smoking and health.

Stockman has now proposed large cuts for almost all the government's domestic agencies in an effort to restrain the projected 1983 deficit, which OMB now says will otherwise exceed $150 billion. Schweiker is one of several Cabinet members appealing these cuts to the president, in a process expected to last until Christmas.

Head Start, authorized in 1965 as part of the Johnson administration's war on poverty, has been one of the most popular of all social programs, especially among minority groups.

Schweiker in his letter warned that "It is not reasonable to expect Congress to agree to incorporating Head Start into this block."

Early this year, the White House said Head Start, serving about 374,000 children, was one of seven essential social programs safe from the budget ax.

The new OMB plan, according to sources, calls for shifting one-quarter of the Head Start funds into the block grant to the states each year for four years.

It also calls for merging the child-abuse and runaway youth programs in the same grant. Schweiker said they would more properly fit in the social services block grant.

In comment on other programs, Schweiker reportedly protested:

A plan to merge six more health programs, including the food program for women, infants and children, into four existing health block grants and then slash funding for all the blocks combined to $1.869 billion in fiscal 1983.

He objected to including the child-health screening and developmental disabilities programs in the health blocks.

In addition, he said $1.869 billion was far too low, a one-third cut from what all the programs in the proposed blocks (including the six additions) had received as individual programs in fiscal 1981.

Stockman-proposed cuts in the National Institutes of Health and in alcohol, drug abuse and mental health research.

Schweiker said the cuts "would be seriously disruptive to continued progress in biomedical research," and demanded restoration of $172 million to put NIH at $3.75 billion and alcohol-drug-mental health research at $300 million.

An $86 million cut planned by Stockman in Schweiker's $638 million request for Indian health services.

Schweiker said the Indian health program "reflects our treaty obligations" and restoring the money would allow HHS "to fulfill its obligations without a reduction in services."

An OMB plan to cut direct activities of the Centers for Disease Control, "a center of excellence unequaled anywhere else in the world," from about $242 million to about $197 million.

The cut, he said, "would erode our ability" to reduce levels of "infectious and other diseases."

An OMB plan to phase out the Public Health Service Commissioned Corps.

An OMB plan to halve the $103 million Schweiker requested for St. Elizabeths Hospital