A conservative who recently resigned after six years on the advisory panel of the antiabortion American Life Lobby has been put in charge of the government's family planning programs.

Dr. Gary E. Crum stepped down from the advisory panel last month to become director of the Health and Human Services Department's Office of Family Planning. He is the second person with links to the antiabortion movement to receive a Reagan administration appointment to a high-level family planning job at HHS.

In February, Marjory E. Mecklenburg, who was cofounder of the American Citizens Concerned for Life, resigned as deputy assistant secretary for population affairs after four years in the job.

Unlike Mecklenburg, Crum has long experience in public health policy and planning. Before his appointment, he was an associate professor in the Department of Health Services Administration at George Washington University.

But his appointment has raised fears among family planning groups about the future of Title X, the government program that provides contraceptive services to low-income women and teen-agers.

The American Life Lobby has pledged to kill the program, arguing that it promotes teen-age promiscuity and that family planning clinics illegally use Title X funds to provide abortions.

This year, the program will channel $142.5 million to 5,000 state, local and privately operated family planning clinics around the country, funds that supporters say are vital to curbing the rise in the number of teen-age pregnancies.

"We are concerned that Crum has not disassociated himself publicly from the views of the American Life Lobby," said Faye Wattleton, president of Planned Parenthood Federation of America.

Crum's appointment last month came as antiabortion legislators, led by Sens. Jesse Helms (R-N.C.) and Orrin G. Hatch (R-Utah) and Reps. Jack Kemp (R-N.Y.), Christopher H. Smith (R-N.J.) and Henry J. Hyde (R-Ill.), succeeded in blocking the Title X authorization for the next three years.

Through an HHS spokesman, Crum said yesterday that he supported the Reagan administration's position that Title X should be eliminated and the funds folded into block grants to the states for "primary care."

Crum added that he supports the full range of family planning services. "Parents should be able to fully determine the timing and spacing of their children," he said.

Family planning groups such as Planned Parenthood argue that more than 800,000 unintended pregnancies were averted in 1981 -- 425,000 of them among teen-agers -- as a result of the Title X program. During the 1970s, they estimate that 2.3 million unwanted births were prevented.

A detailed defense of Title X issued this week by Planned Parenthood said that 42 percent of the 9.5 million low-income women and 43 percent of the 5 million sexually active teen-agers who needed subsidized family planning services in 1981 did not obtain medically supervised contraceptive care.

But antiabortion groups say they intend to lobby fiercely to kill the program. "We want to totally dismantle Title X," said Paul Brown, chief executive officer of the American Life Lobby. "There are better places for taxpayers' dollars than IUDs and pills for our kids.