A federal judge in Denver has issued a preliminary injunction against President Reagan's new antiabortion rules for federally funded family planning programs.

The ruling, which applies only to three family planning groups in Colorado and Utah, is the first step in an expected lengthy legal battle that could eventually reach the U.S. Supreme Court.

The three clinics and the Planned Parenthood Federation of America sued in U.S. District Court in Denver to block the new regulations from going into effect March 3.

Federally funded clinics are already prohibited by the 1970 Family Planning Act from using any funds to perform abortions.

Under the proposed new rules, a clinic receiving support from the $139 million-a-year Federal Family Planning Program would be barred from informing a pregnant woman that keeping the baby, putting it up for adoption or having an abortion are options for handling an unintended pregnancy. It also would be barred from referring her to an outside abortion clinic if she requested.

Opponents of the rules contend the 1970 act intended to allow a listing of options, including abortion, and to permit referrals.

But the Reagan administration asserts that informing a woman of these options abets abortion and thus is counter to the specific provision barring the use of federal funds for abortion.

U.S. District Court Judge Zita L. Weinshienk ruled Monday night that application of the new rules to Planned Parenthood of the Rocky Mountains, Planned Parenthood Association of Utah and Boulder Valley Women's Health Center should be blocked, pending a full hearing on whether the rules are legally valid.

Similar lawsuits have been filed in Massachusetts and New York.

Weinshienk said the new rules contradict the intent of the 1970 Family Planning Act; interfere with a woman's fundamental right under the Fifth Amendment to terminate a pregnancy and her right under the First Amendment to obtain the information needed to exercise her right to terminate pregnancy; and impose an unacceptable straitjacket on the physician's obligation to provide information to a woman.

Eve Paul, vice president of the Planned Parenthood Federation of America, said the organization "is confident that these dangerous and misguided regulations will never be put into effect."