WASHINGTON — A week before President Clinton delivers his budget blueprint for 1995, half the Senate is already fighting to protect a program that helps millions of low-income families heat their homes.

Fifty-one senators, including Majority Leader George J. Mitchell of Maine, have written the president to urge him to reconsider deep cuts in the Low Income Home Energy Assistance Program, or LIHEAP.

The letter, dated Jan. 14 but released Friday, says a reduction in LIHEAP of 30 percent or more “simply is unacceptable.”

Congress has set aside $1.475 billion for LIHEAP in 1995. But congressional aides say the administration has hinted it would seek to cut the program to $730 million when it proposes next year’s budget on Feb. 7.

A spokesman for the Department of Health and Human Services, which runs LIHEAP, declined to comment Friday on the budget before its release.

In their letter to the White House, the senators acknowledged that Clinton faces enormously difficult budget choices. But they said LIHEAP has already been pared back enough from its peak funding of $2.1 billion a decade ago.

LIHEAP, created during the energy crisis of the late 1970s, is one of many programs competing for tight dollars in the HHS budget. Among the other programs is Head Start, which is targeted for a significant increase from this year’s $3.3 billion.

According to the lawmakers, LIHEAP benefits reach fewer than 25 percent of all eligible households. Spending on the program this year is nearly $1.44 billion.

“Home energy costs consume an unreasonably high portion of what disposable income the poor have,” the senators said, pointing to a recent study at Boston City Hospital that found emergency room visits related to malnutrition consistently peaked immediately after the coldest weather.

“The conclusion the researchers drew is that families had little money to buy groceries after paying their utility bills,” the senators wrote to Clinton. “According to the report, `parents know their children will freeze to death before they starve.’ How can we expect Head Start and similar programs to work if children live in such circumstances?”

LIHEAP distributes funds to the states based on a formula involving local energy costs and poverty rates.

States use the money to help poor families pay for fuel, avert a shutoff or reconnect their utilities, and for weatherization. A few states run summer cooling programs under LIHEAP.

Last winter, the program reached 5.2 million households, down from a peak of 6.8 million households in 1985.