A majority of Virginians support an across-the-board freeze on federal spending, the MX and voluntary school prayer, while they oppose economic sanctions against South Africa, according to a survey by Sen. Paul S. Trible Jr. (R-Va.).

The questionnaire, distributed by Trible earlier this year, was answered by 100,000 Virginians. Trible recently released the results of that questionnaire.

A majority (62 percent) said that the most important issue facing the nation is the federal deficit. The need for an arms control agreement was next (13 percent), and then tax reform (7 percent).

An across-the-board freeze on federal spending was supported by 65 percent, and a constitutional amendment requiring a balanced budget was favored by 71 percent. Some 63 percent felt that the president should be given line-item veto authority, which would allow him to veto part of a spending package and approve the rest.

Asked to choose between reductions in defense and nondefense programs, 63 percent felt that both defense and nondefense spending should be reduced, 27 percent said that only nondefense spending should be cut, and 10 percent said only defense should be reduced.

On foreign affairs, 64 percent were opposed to a ban on American investments in South Africa as a policy to eliminate apartheid. Aid to anti-Sandinista rebels in Nicaragua was supported by 59 percent. Increasing American aid to famine victims in Africa was supported by 65 percent.

The MX missile was supported by 62 percent, and the antimissile defense system in space was supported by 67 percent.

A constitutional amendment allowing voluntary prayer in public schools was supported by 68 percent.