Nancy Harvey Steorts, one of the highest-ranking women in the Reagan administration, resigned yesterday as chairman of the Consumer Product Safety Commission.

Steorts, who announced at a press conference that she will leave Jan. 5, said the time had come for her "to move on to new challenges." She said she has "several real good" options to consider in the private sector.

Administration officials and several sources close to the commission said that Terrence M. Scanlon, an agency commissioner, most likely would succeed Steorts. Scanlon, a 45-year-old Democrat, served as CPSC vice chairman for the year ended June 1. He served as a staff assistant to presidents John F. Kennedy and Lyndon B. Johnson.

Steorts' term on the commission expired Oct. 26, and the White House had taken no action to reappoint her. She became CPSC chairman in August 1981.

Steorts is the second high-ranking Reagan administration regulator to resign this week. Environmental Protection Agency Administrator William D. Ruckelshaus announced his departure Wednesday.

Congressional sources and consumer groups expressed disappointment yesterday with Steort's departure and the reports that Scanlon will replace her.

"During her tenure at CPSC, Chairman Steorts had a solid record of consumer protection, was willing to take on the Reagan administration regarding staff and funding cuts at the agency and supported such legislative initiatives as the Toy Safety Act and the Amusement Park Ride Safety Act," said Henry A. Waxman (D-Calif.), chairman of the House subcommittee with jurisdiction over the agency.

Although consumer groups initially disapproved of Steort's appointment and contended that she set an anti-regulatory tone at the commission, they generally approved of her voting record.

"When it came down to the tough and important votes, Steorts voted for consumers," said Mary Ellen Fise, product safety director of the Consumer Federation of America.

During her term as chairman, Steorts voted against a policy, ultimately rejected, allowing export of products the CPSC ruled unsafe.

She also fought to ban urea formaldehyde foam insulation, which the CPSC declared unsafe; opposed endorsement by the agency of voluntary product safety standards, and supported legislation to allow speedier recalls of unsafe toys.

"I fear it is because of this record of consumer protection that the Reagan administration has refused to reappoint her, and is instead seeking a replacement more amenable to its goal of destroying this small consumer protection agency," Waxman said.

Consumer groups said Scanlon's appointment would be a setback. Scanlon, who voted against Steorts' position on many issues, was the only commissioner who voted to allow companies to export products that the CPSC had deemed unsafe.

He has been a major proponent for CPSC endorsement of voluntary standards for industry, which an agency source said was opposed by other commissioners, the Federal Trade Commission and the White House Consumer Affairs Office. Opponents of the idea said it would give industry a seal of approval for minimal safety standards.

Scanlon opposed Steorts' support for giving CPSC power over safety standards for fixed-site amusement rides in parks such as Disney World, which now are unregulated.