Secretary of Transportation Elizabeth Hanford Dole yesterday praised Metro's new plan for completing 89.5 miles of the proposed rail system, calling it a "highly positive step."

Nevertheless, in her first comment on the transit agency's proposal, Dole stopped short of saying whether the Reagan administration would approve the plan. The administration has limited federal construction funds to 76.4 miles of the proposed 101-mile Metro system.

The new Metro plan calls for using federal funds previously authorized by Congress to complete 89.5 miles, including a long-delayed Green Line branch connecting Fort Totten with Greenbelt in Prince George's County and a Yellow Line spur to a proposed Van Dorn Street station in Alexandria.

Metro officials have said they will eventually seek an additional congressional authorization of more than $1 billion to complete the rest of the planned 101-mile system.

Dole cited the new Metro plan in a speech to the American Public Transit Association, which opened its annual meeting at the Convention Center here yesterday. The association, which represents the nation's transit systems, is holding its three-day conference in Washington for the first time in recent years. About 8,000 officials are expected to attend the sessions.

Shortly after Dole spoke, 14 handicapped demonstrators, including several in wheelchairs, were arrested outside the Convention Center, according to D.C. police. The protesters were charged with blocking entrances to a public building and disorderly conduct.

Since last week, members of a Denver-based group called ADAPT, an acronym for American Disabled for Accessible Public Transit, have staged demonstrations here to demand improved access to buses and trains for handicapped patrons in transit systems throughout the nation. The group contends that all buses should be equipped with special lifts for wheelchairs.

In her speech, Dole expressed "deep concern for the plight of the handicapped" and argued that proposed regulations now under review by federal officials would provide "adequate access" to transit services for disabled riders.

The federal proposals are less stringent than those sought by ADAPT, but they appear largely acceptable to the transit association. Several years ago, the association sued federal officials to block stricter requirements.

Jack R. Gilstrap, the association's executive vice president, said the new proposals would provide flexibility for local governments. "We support the local option concept," Gilstrap said.

Dole described the 89.5-mile Metro plan as evidence that "there can be progress" in state and local efforts to devise new methods to finance transit projects.

The Metro plan still must be ratified by county and city governments, in the Washington area, and Dole indicated the administration would withhold a decision on the plan until local governments act.

Federal financing of the nation's transit systems is expected to be a focus of debate at the convention. Dole indicated no shift in policies, and she reiterated the administration's reluctance to subsidize operating costs, a controversial issue.

"The most crucial issue facing public transit today is funding," Metro General Manager Carmen E. Turner told the conference.

Twelve of the handicapped demonstrators were arraigned before a U.S. commissioner and released pending further hearings. Two protesters forfeited collateral of $10 each. Police said one policeman suffered several broken fingers after being rammed by a protester's wheelchair.