WASHINGTON (AP) _ Teen-age pregnancy is an ''explosive and complex'' issue that a lot of state legislatures around the country are discussing but few are doing much about, a specialist on the issue says.

''This is a crisis, in my opinion,'' Lula Mae Nix, executive director of the National Institute for Adolescent Pregnancy and Family Services at Temple University, said at a news conference Wednesday.

Noting that about 1 million American teen-agers get pregnant every year, she said, ''The problems posed by teen births can no longer be ignored by state legislators or taxpayers who carry the economic burden.''

The problem is ''an explosive and complex issue that strikes many sensitive nerves'' because it involves such matters as abortion rights, contraception, sex education and teen-age sexuality, said Nix, who headed the federal Office of Adolescent Pregnancy Programs in the Carter administration.

''The long-term negative consequences of teen-age pregnancy and parenting are immense, both in personal and public cost,'' she said. ''Despite the challenge to do something, the majority of states have yet to develop comprehensive policies and legislative initiatives to deal with the problem.''

A report by consultant Vukani Magubane on a survey of legislation found that in the 34 states that responded to a questionnaire sent out last May, 121 bills relating to teen-age pregnancy and parenting were introduced. Of those, 51 failed, 48 passed and 22 were pending.

But Nix cautioned: ''Because a state has introduced a great many pieces of legislation does not make it a model.''

Many legislative approaches to deal with the problem ''have been fragmented and only a few states have done or attempted more compthe issue for representatives from state governmental and other agencies begins today, and the participants will receive copies of a model legislative package developed by the institute, Nix said.

A comprehensive approach, she said, must address such areas as education on sex and family living, continuation of schooling for teen-agers who become pregnant, good health care and nutritional information.

Another issue to be addressed, she said, is child care. ''Many of these young girls - 13, 14 - know nothing about taking care of a baby and that can lead to child abuse,'' she said. In 1982, about 27,000 American girls under age 15 got pregnant, she said.

''More adolescents are engaging in sex at an earlier age, some as young as 9 years old,'' she said. ''By their 15th birthday, 5 percent of teen-age girls and 17 percent of teen-age boys report having had intercourse. By the time they have their 18th birthday, these numbers have grown to 44 percent of girls and 64 percent of boys who are sexually active. The 1970s sexual revolution, in short, has moved from the college campus to high schools and has now filtered down to the junior high and grade school levels.''

It is in the states' best interests from an economic as well as a social point of view to confront the problem directly, she said, citing Ohio estimates that a teen mother and child receiving Aid to Families with Dependent Children cost state residents over $9,000 in the first year in various forms of aid, food subsidies and medical care.