WASHINGTON--State Department Officials here feel that South Vietnam's boycott of the new phase of the Paris peace talks beginning Wednesday will probably not hold up negotiations for a ceasefire and withdrawal of foreign troops from Vietnam.

Although President Johnson spoke in his bombing halt-broadcast Thursday as though attendance of both the South Vietnamese and the National Liberation Front was assured, South Vietnam's President Thieu announced a day later that his government would not attend the session on Wednesday.

The United States has said it will discuss unilaterally any issues in which the United States and North Vietnam are primarily involved. Apparently Washington feels the important question of troop withdrawal falls in this category.

Secretary of State Dean Rusk, speaking at a news conference Friday, said he was certain that South Vietnam would join the talks sooner or later.

Persistent Talk

Talk about a ceasefire has been almost as persistent over the last three years as talk about the halt in the U.S. bombing of North Vietnam. The United States generally has taken the position that a ceasefire would need detailed agreement between Communist and allied leaders, and that it could not be part of a bombing-halt plan for this reason.

The United States has taken the new position, however, that establishment of a ceasefire could be the first order of business when the Communist representatives got down to serious peace negotiations.

The developing U.S. position now, it is learned, is that the major objective of the next round of negotiations should be to arrange for withdrawal of all foreign troops from South Vietnam, including the forces of North Vietnam and the United States.