Several times during the past year political writers have declared the presidential honeymoon to be over, only to discover that President Reagan had won another extension. With his State of the Union message this week the grace period now seems to have ended -- at least on Capitol Hill.
All sides continue to give him credit for eloquence following his Jan. 26 speech, but even some of the President's staunchest congressional supporters are voicing keen doubts about his program. They worry chiefly about the gigantic deficit that the President acknowledged is edging toward $100 billion.
Mr. Reagan gave notice that he will continue his effort to save the economy by cutting taxes and trimming federal spending, while at the same time strengthening the nation's defense. And he proposed a long-range program that would turn over 40 federal programs to the states over an eight-year period.
He offered no ''quick fix'' to unemployment or the federal budget's sea of red ink.
''We're going to have trouble with a deficit in the range of what the President's talking about,'' said House minority leader Robert H. Michel of Illinois, responding to the speech. Calling himself a good conservative Republican, he said that he would find it hard to vote for such a big deficit.
Moreover, he predicted that Congress would not go along with the President if he pushes for big new increases in military spending.
Democratic leaders have predictably lambasted the President for failing to deal with unemployment and high interest rates. A Democratic Party documentary-style television show, aired just after the President's speech Jan. 26, hinted darkly of a new depression.
But most important to Reagan's programs will be the members of his own party. Republican unity in both houses of Congress secured the Reagan victories last session, with the help of conservative Southern Democrats. Now many Republicans from hard-pressed Northern and Midwestern cities are sending up signals that they may not be able to go along for the ride this time.
One of those so-called ''gypsy moth'' Republicans, US Rep. William S. Green of New York, voted with the President a little more than half the time last session. This time he's not sure. Cuts made last year hit hardest on social programs of ''great importance to us in the North and Midwest,'' and more cuts ''would be a problem for us,'' he says, particularly if the administration does not look for savings in defense.
''Most of us have supported the increase in the military pay,'' says Congressman Green of his fellow gypsy moths. ''But a lot of us question whether we need five ways to respond to a Soviet attack.''
Like all House members, Northern and Midwest Republicans must face re-election next fall.
Rep. Claudine Schneider (R) of Rhode Island says she supports much of the Reagan effort. But will she vote for cuts in social programs? ''It all depends on whether those program cuts are suitable to Rhode Island's needs,'' she says. ''My allegiance is first to the people I represent and second to Ronald Reagan.''
President Reagan's ''new federalism'' proposal, meanwhile, is finding a mixed reception on Capitol Hill. Some Democrats dismiss it as a distraction. ''It's something we ought to think about in the next decade,'' said House Budget Committee chairman James R. Jones (D) of Oklahoma. It says nothing to the couple who can't buy a house or the unemployed worker or small businessman, he told reporters after the speech.
Senate majority leader Howard H. Baker Jr. (R) of Tennessee praised the plan as a ''logical next step.'' And House minority leader Michel hailed it as a ''long-range cure to long-range ills of the country.''
Although so far Mr. Reagan has unveiled only the general outlines, the new federalism proposal will spark debate for months to come. Congress is taking a wait-and-see attitude.
Rep. Beryl Anthony Jr. of Arkansas, a Democrat who frequently voted with the President last session, says he will watch the details of that program carefully. ''It could have regional bias,'' he says, with all the advantages going to resource-rich states.
The one unknown factor that could shake that assertion is the Reagan ability to communicate his wishes to the public. ''He was speaking over our heads to the American people,'' concluded Congressman Michel after the State of the Union message. He added that pressure from constituents, so evident last year, could strongly influence Congress to back the President again in 1982.