President Reagan, following '80 strategy, leans toward right as campaign opens

His economic advisers may be squabbling back in Washington. His foreign policy may be unraveling in Lebanon. His critics in Congress may be up in arms over budget deficits.

But President Reagan, with buoyant gait and cheerful smile, is staying above the fray, skillfully choosing campaign audiences in the hinterlands and preaching a message of economic uplift, America's rebound, and renewal of bedrock values.

Celebration of his 73rd birthday in his hometown of Dixon, Ill., on Monday gave the President another colorful opportunity to dominate the television media and sound a note of optimism.

''The reason I came home today was not to celebrate my birthday, but to celebrate Dixon and America,'' he told a crowd in the gymnasium at Dixon High School. ''Honor, integrity, and kindness do exist all across our land. There is a zest for life and laughter.''

Later, in a speech scheduled for delivery at his alma mater, Eureka College, Mr. Reagan reviewed his boyhood experiences, traced the nation's economic history over the last 60 years, and again assailed government as an ''obstacle to economic progress.'' He also renewed his call for arms reduction with the Soviet Union, while noting the ''struggle between democracy and totalitarianism'' and today's intellectual ''disenchantment with communism.''

As he nostalgically marked his birthday in his hometown, political observers agreed that the President has effectively defused the issue of age as a campaign issue. Although he would be almost 78 when he completed a second term - the oldest American president in office (Eisenhower left office when he was 70) - Reagan is not perceived as old or elderly.

On the contrary, his ruddy countenance beams with good health, and he projects vigor and even youthfulness. Polls show that the vast majority of Americans say Reagan is not too old to run for a second term.

Politically, the President has gotten a fast start out of the blocks. In the first 10 days since announcing his candidacy - in addition to presenting his 1985 budget - he has addressed an array of groups, including women and evangelicals.

Today he is scheduled to address the National Association of Secondary School Principals in Las Vegas, Nev., and join a local Republican fund-raising luncheon before flying to his California ranch for a five-day vacation.

While most of these speeches are ''official'' and therefore are not paid for by his reelection campaign committee, they are for all intents and purposes political stump speeches designed to rouse specific constituencies. That is the advantage of an incumbent president. Whatever he does, he does as President and can turn presidential visibility and actions into potential political advantage.

Early in the election season, the President seems to be focusing largely on his hard-core conservative supporters - a constituency that has not been happy with the Reagan record on the social agenda. Hence his stress on such themes as prayer in the schools, tuition tax credits, and anti-abortion legislation.

As the campaign moves toward election day, Reagan is expected to shift toward the political center, focusing more on the mainstream Republican themes and dwelling less on the controversial conservative issues that could cost him votes. A similar strategy was pursued in the 1980 campaign.

''The conservative right is most likely to want to hear his message,'' says Austin Ranney, a political expert at the American Enterprise Institute. ''But the Reagan strategists don't want permanently to feature such issues during the campaign. So Reagan is starting off getting the true believers enthusiastic; then he will go on to deal with foreign policy and other issues that aim at the broader population. Strong statements on abortion can be helpful now but could be damaging later.''

As for the feuding among his economic advisers over the huge budget deficits, Reagan deftly manages a posture of detachment. The general public is not knowledgeable about or interested in such bureaucratic infighting, political analystssay. Unless the President were to become embroiled himself, the Regan-Feldstein-Stockman controversy has little impact on voters.

Whether the President can escape the liabilities of a $180 billion deficit is another matter, however. The general political view seems to be that the issue is an abstract one for most Americans.

Reagan will not necessarily suffer politically from the deficits, say analysts, unless their negative effects are actually felt nearer election time - in higher interest rates, for instance.

Reagan, in any case, did not shy away from the subject in the heartland of Illinois, where he again called for a constitutional amendment to balance the budget. ''Politicians at the national level must no longer be permitted to mortgage your future by running up higher and higher deficits,'' he said in the speech prepared for delivery at Eureka College. ''The time has come to force government to live within its means.''

Taking the political offensive with his customary rhetorical flourish, President Reagan declared that the ''juggernaut of big government has now been slowed,'' and that ''we've brought skyrocketing spending back to earth.'' During the Reagan presidency, federal spending and budget deficits have reached their highest levels ever.