At a time when most government social programs are about to be slashed, one of the Senate's new conservatives has proposed a $30 million program to promote chastity among teen-agers.

Sen. Jeremiah A. Denton (R-Ala.), author of the measure, believes "adolescent promiscuity is emotionally and morally damaging," counterproductive "to the normal maturation process, and results in a high risk of pregnancy."

Instead of promoting birth control, sex education and legal abortions, Denton says the government should promote chastity among teen-agers and encourage those who get pregnant to put the babies up for adoption.

His bill would write into law a new definition for promiscuity. "Promiscuity," it says, "means having sexual intercourse out of wedlock."

The bill's purpose is "to promote self-discipline and chastity, and other other positive, family-centered approaches to the problems of adolescent promiscuity and pregnancy."

But it is unclear exactly how the bill would do so except through "a variety of integrated and essential services provided to adolescents and their families by other family members, religious organizations, voluntary associations and other groups in the private sector."

Apparently this means the government would finance programs promoting chastity among teen-agers and adoption services for unamrried teen-age mothers. Currently, only 4 percent of teen-age mothers put their children up for adoption. Denton's bill says.

The bill, co-sponsored by Chairman Orrin G. Hatch (R-Utah) of the Labor and Human Resources Committee, would replace the current teen-age pregnancy program, keeping some of its services, such as pregnancy and venereal disease testing, and health counseling.

But it would prohibit groups such as the Planned Parenthood Federation from receiving any funds under the program because they offer abortion counseling.