WASHINGTON (AP) _ George Washington delivered his farewell address to a Philadelphia newspaper, Lyndon Johnson and Gerald Ford delivered theirs to Congress and Ronald Reagan is turning to the medium of which he is most the master - television.

Reagan's swan song as president will be delivered at 9 p.m. EST tonight from the Oval Office and will be carried by the networks.

Asked today for a preview of his speech, Reagan told reporters, ''I'm just trying tonight to have a conversation with the American people.''

The White House press office said the address, expected to last about 20 minutes, would be the 43rd television speech of Reagan's presidency.

''We expect it to be a very personal kind of look at what President Reagan tried to do, and what he sees as his accomplishments, and the problems ahead,'' White House spokesman Marlin Fitzwater said Tuesday.

''It will be an opportunity for him to talk directly to the American people as he has done so often in the last eight years.''

Indeed he has.

It was through this forum that the president:

- Helped generate the steam to push his tax cuts through Congress.

- Sprang his Star Wars plan for a space-based defense against missiles.

- Mourned the death of the Challenger space pioneers.

- Defended his decisions in the Iran-Contra affair.

Kenneth Duberstein, the White House chief of staff, said this morning on NBC's ''Today'' program the speech is intended to be ''a personal conversation that the president really wants to have with the American public.''

Duberstein predicted the address would include ''a little bit of nostalgia, pointing to the accomplishments, pointing to some of the vision that Ronald Reagan brought to the Oval Office and to the presidency in 1981 and some vision that he has for continuing the Reagan revolution.''

''I think you're going to hear some anecdotes and some stories but you're going to hear Ronald Reagan talking about how fundamentally America has been changed, the world has been changed,'' Duberstein said.

''And I think you may see some advice for the American people in the years to come that may be a little bit different than you may have anticipated.''

The former radio announcer, movie actor and after-dinner speaker came to the White House with more television-related experience than any of his predecessors. His 1964 television speech for Barry Goldwater helped catapult Reagan into two terms as governor of California, where he continued to sharpen his television skills as well as gaining experience in government.

In his first major televised speech from the Oval Office, he outlined his tax reduction program on July 27, 1981, using charts and a pointer to make his case that the administration plan was more fair than that proposed by Democrats in Congress. He ended, as he would so often, ''Thank you, God bless you, and good night.''

But his statement from the Oval Office on Nov. 13, 1986, that the arms sent to Iran ''could easily fit into a single cargo plane'' and did not constitute a swap of arms for hostages, failed to go over in Congress. Reagan later had to admit mistakes had been made.

Sometimes he had surprises up his sleeve. His speech on March 23, 1983, announcing that he was ordering a study of what came to be known as the Strategic Defense Initiative, or Star Wars, was news to many of his key advisers.

His speech on the Challenger explosion on Jan. 28, 1986, was one of his shortest, only 11 paragraphs, and is often cited as an example of Reagan at his most eloquent. Speaking only a few hours after the disaster, he told the families of the crew members, ''They wished to serve, and they did,'' and added, ''Nothing ends here; our hopes and our journeys continue.''

Tonight's speech is likely to be short on news, but it follows a tradition of farewell addresses that has been followed by many previous presidents from George Washington to Jimmy Carter.

Washington's farewell address attacked ''the spirit of party'' and warned against foreign entanglements. Washington released it to one newspaper, the American Daily Advertiser, and papers throughout the new nation quickly picked it up. It has become a classic American text that is still read annually in Congress on Washington's birthday.

The most celebrated presidential address of the television era is Dwight Eisenhower's on Jan. 17, 1961, in which the old general warned, ''In the councils of government we must guard against the acquisition of unwarranted influence, whether sought or unsought, by the military-industrial complex.''

Johnson and Ford, both former congressional leaders, chose to make their final speeches in the form of State of the Union addresses to Congress, as some other presidents have done.

Carter spoke from the Oval Office on Jan. 14, 1981, six days before Reagan took over. The Democrat promised Reagan his support ''to the very limits of conscience and conviction'' and warned of the need to reduce the ''horrifying danger'' of nuclear arms stockpiles.

Fitzwater said Reagan spent several hours this week working on his speech.

If it is like most presidential speeches, he will also have had some help from the speechwriting office. But then that's nothing new. According to Washington biographer James Thomas Flexner, the nation's first president worked from a draft by his secretary of the treasury, Alexander Hamilton.