A new radio ad launched this week in Maryland by the Reagan-Bush campaign credited the president for dredging the port of Baltimore, even though harbor dredging was delayed three weeks ago when Reagan threatened to veto a congressional measure containing federal funds earmarked for Maryland's most sought-after public works project.

The ad, aired on seven Baltimore radio stations and a handful of others around the state, cited reasons Reagan has been good for Maryland, including that "the harbor is being dredged."

A spokesman for the Reagan-Bush campaign in Maryland, Carol Hirschburg, yesterday confirmed that the ad was inaccurate and said it was supposed to be clarified before going on the air. She said the incorrect version, first aired Tuesday, would be pulled from all stations immediately. A spokesman at one of those stations, WITH-AM, confirmed that the ads there had been pulled.

Bo Denysyk, executive director of the state Reagan-Bush campaign, said the intent of the ad was to show that Reagan supports harbor dredging.

"Perhaps the ads were not as explicit as we would like," he said yesterday. "They probably used language a little too loosely. Maybe they were trying to be clever."

The ad was made by a New York advertising agency, based on information from the national Reagan-Bush campaign, according to Denysyk. He said the Maryland campaign told national Reagan-Bush officials that several points should be included in ads tailored for Maryland, including that "the president supports harbor dredging."

Denysyk said he did not know which New York agency produced the ad and that Maryland campaign officials had no direct contact with the agency.

Harbor dredging cropped up as an issue in the presidential campaign in Maryland when Reagan visited Baltimore on Columbus Day and proclaimed his support for the project. The next day, however, he threatened to veto Congress' continuing budget resolution if it included a host of water projects, including funds for the Baltimore port. Congress agreed to drop the water projects.

Immediately thereafter, top Maryland Democrats who support Walter F. Mondale, including U.S. Sen. Paul S. Sarbanes and Rep. Barbara A. Mikulski, attacked Reagan for derailing a project that has tremendous economic significance to the state.

Harbor dredging has been a controversial issue in Maryland for 14 years, ever since the state's congressional delegation first attempted to get federal funding to deepen the 45-foot Baltimore port. Deepening the port would allow fully loaded super coal carriers to enter for the first time, bringing jobs and lucrative coal export profits.

Although most of the state's congressional delegation heartily supported dredging, Rep. Clarence D. Long, a Baltimore County Democrat, stubbornly opposed it.

This year, however, Long agreed to join his colleagues in support of deepening the harbor, and until Reagan's threat to veto the budget measure it appeared the project would finally get under way.