The Reagan administration, in a presidential determination made public late Monday, has castigated Ethiopia's human rights record in extremely strong terms and accused it of deliberately adopting policies that have "no doubt caused vast and unnecessary human suffering, including starvation."

But it has decided against imposing a trade embargo on the Marxist East African country, recently mandated by Congress in certain circumstances, because it found that the government there is not presently pursuing a "policy of starvation."

An amendment to the International Security and Development Cooperation Act of 1985 called for a presidential determination by last Saturday on whether Ethiopia is conducting "a deliberate policy of starvation of its people" and has failed to grant citizens "fundamental human rights."

If Ethiopia had been judged guilty on both counts, the administration would have been obliged to impose a trade embargo and halt the export of U.S. goods and services except for emergency drought-relief assistance.

In the justification for its decision not to impose sanctions, the administration called Ethiopia's respect for human rights "deplorable" and said its political, economic and military policies, particularly its resettlement program for famine victims, had caused vast suffering.

It added, however, that "the available evidence does not justify a determination that the government of Ethiopia is at this time 'conducting a deliberate policy of starvation.' " The congressional directive did not require imposing sanctions because of past Ethiopian conduct and policies, it added.

Attacking Ethiopia's human rights record, the report charged that many of nearly 500,000 peasants taken from the drought-stricken north to richer lands in the southwest had been "forcibly separated" from their families and taken under "inhumane conditions" to sites in "primitive wilderness areas."

"Veterans of the resettlement campaign who have escaped report beatings, murder, imprisonment, deprivation and what they consider enslavement in a highly regimented work environment where mortality rates are exceedingly high," the report said.

"The inhumane resettlement program diverts from the food-relief effort badly needed transport and logistical support and supplies," it added.

While the report was sharply critical of Ethiopia's famine-relief efforts, it said the government there had taken actions to correct the situation "in response to pressure from the U.S. and other donors."

It noted an Ethiopian decision to allow a small feeding program by U.S. voluntary groups behind rebel lines in contested northern areas. It also said the government had reduced the pace of resettlement and that recent evacuation of relief camps was "more humane," with returnees given food and seed.

It said the U.S. government would continue to monitor these activities and to press Ethiopia "to make further sustained improvements."