D.C. police officer Thomas K. Delahanty, who has not returned to duty since he was shot during the assassination attempt on President Reagan last March 30, has been retired from the police department on full disability.

Delahanty said he received word over the weekend that the city's police and firefighters' retirement board approved his departure from the force after 18 1/2 years of service. There was no opposition to his retirement petition. He will receive two-thirds of his regular salary, tax-free.

Delahanty, 48, was assigned to special duty at the Washington Hilton, where he and two other persons were gunned down along with the president. John W. Hinckley Jr. has been accused of attempting to assassinate Reagan.

The police officer suffered rerve damage in his left arm from a shot in the shoulder. The bullet ricocheted off his spinal cord.

By coincidence, the announcement of his retirement came the same day as presidential press secretary James Brady returned home from George Washington Hospital, where he had undergone treatment for severe wounds suffered in the same shooting episode.

Delahanty said he has no immediate plans, and will continue to live in Beltsville. His wife is scheduled to retire in January from the C & P Telephone Co.

Former vice president Spiro T. Agnew is preparing to challenge a quarter-million dollar judgment against him in a Maryland court, contending that the state never proved he accepted kickbacks while he was governor.

Agnew's lawyer, T. Rogers Harrison, said he would ask the state Court of Special Appeals to overturn the judgment ordered in May by Judge Bruce C. Williams in Anne Arundel County Circuit Court. He said he would raise at least a dozen legal issues.

Agnew was ordered by the court to repay the state $ 147,500 he allegedly received in bribes from highway contracting firms, plus $ 101,235 interest.

Work has gotten under way on the controversial $ 154 million Georgetown waterfront commercial, residential and office project being undertaken by the Western Development Corp. With a court challenge to the project removed, the firm now has the necessary permits to build on the six-acre site now occupied partly by the Super Concrete Co. Initial work involves cleaning the site, with actual construction set to begin in January, a company spokesman said.

The D.C. Public Service Commission announced that it will wait until at least Dec. 5 to set the date that new taxicab rates will go into effect in the city.

The PSC published a notice in the D.C. Register, the city's weekly compendium of official announcements, giving a 15-day notice of its intention to take final action on the increase, ranging from 15 cents to 25 cents per trip under the zone fare system. The amount of the increase was announced Nov. 6.

It's official: Lt. Gov. Charles S. Robb is now Virginia's governor-elect. The state Board of Elections in Richmond yesterday certified the results of the Nov. 3 balloting in which Robb, a Democrat, defeated Republican Attorney General J. Marshall Coleman for Virginia's top job.

Final results varied only slightly from the unofficial returns reported in the news media the day after the election.

Robb received 760,357 votes (53.5 percent) to 659,398 (46.4 percent) for Coleman. Only 856 write-in ballots were cast, including 198 from Halifax County, the home of black protest candidate Cora Tucker.

In the lieutenant governor race, Democrat Richard Davis received 750,743 votes (55.4 percent) to 602714 (44.6 percent) for Republican Nathan Miller.

For attorney general, Democrat Gerald Baliles got 682,410 (50.9 percent) to the 656,284 (49.1 percent) cast for Republican Wyatt Durrette of Fairfax.

There is political news from Maryland, too. Yvonne C. LaPole of Hagerstown, currently vice chairman of the Washington County Republican Central Committee, has been named secretary of the Maryland Republican Central Committee. She replaces Arlene Baybutt, who has become chairman of the state Republican Women's Federation.

From Oakland, Md., covered with snow from a weekend storm, comes word that the Wisp ski area in Garrett County is scheduled to open for the season next weekend. Located near Deep Creek Lake, Wisp is Maryland's only ski resort.