President Reagan accused Democrats Saturday of ignoring the accomplishments of his Republican administration and "singing the same sad song they sang four years ago."

"To them, it's midnight in America," Reagan said in his first comment on the Democratic National Convention that ended Thursday in Atlanta."To listen to the rhetoric, you would never guess the American economy is the strongest it has been in a decade," he said.

Reagan made his comments in his weekly radio address, delivered from his mountaintop ranch in the Santa Ynez Mountains north of here. The president and first lady Nancy Reagan will return to Washington on Sunday after a weeklong vacation.

While campaigning in Modesto, Calif., Democratic presidential candidate Michael Dukakis had no response to Reagan's remarks. "We want to stress a positive message. That's the idea. They know we're going to have a chance."

Later, Dukakis told reporters in Minot, N.D., "If the Republican Party thinks the way to win an election is basically to tear the other guy down day after day, believe me (running mate) Lloyd Bentsen and I can respond and will respond."

Rep. Beryl Anthony Jr., of Arkansas, who delivered the Democrats' response, said the party's convention enthusiasm was "spreading like wildfire across the prairie."

"After eight years of a Republican administration fueled by selfish and sometimes unlawful motives, the American people are looking for a return to the basic values of common respect, compassion and concern for all," Anthony said.

He cited the plight of workers whose plants have been shut down and farmers who have lost their farms and said Democrats in Congress have been "the safety net for the American people."

Reagan said the Democrats are "covering their tracks" this year because they have found that the liberal policies they have pursued in the past are unpopular.

"You will never hear that `l' word `liberal' from them," he said. "They've put on political trench coats and dark glasses and slipped their platform into a plain brown wrapper.

"While they are saying that government needs to do more of this or more of that, will they also pledge not to raise taxes?" he asked.

"When their party left the White House eight years ago, inflation was at one of the highest levels in American history," Reagan said. "Now, it's under control. Do they want to turn that around?"

Saying that his administration has improved American competitiveness in world markets and improved American-Soviet relations, he repeated, "Do they want to turn that around, too?"

"They said America can do better," the president said. "With that, I wholeheartedly agree. But the people also know that the last time our opponents were in charge, America did a heck of a lot worse."

The president challenged the Democrats also to go forward with the missile defense system known as the strategic defense initiative or "Star Wars," which he called "the one practical way of reducing the threat" of nuclear weapons.

"And while they are talking about the war on drugs, will they also support the death penalty for drug kingpins?" he asked.

"Some people just don't seem to learn," he said. "The American people want to hear straight talk about where our leaders plan to take the country, not personal attacks."

The Reagans have been at their Rancho del Cielo since Sunday, enjoying generally sunny and pleasant weather.

The White House said their son, Ron, and his wife, Doria, had dinner with the president and his wife on Friday and spent the night at the ranch.