Celebrating his first full day of freedom, Lech Walesa, the leader of Poland's outlawed Solidarity trade union, today said he was walking along a political tightrope.

Walesa told foreign correspondents in interviews at his home here that, before his release yesterday, he had received a three-hour lecture from officials at the prosecutor general's office in Warsaw. He did not give details, but they presumably warned him that, under martial-law regulations, he would face arrest if he attempted to conduct union activity.

Walesa, a one-time electrician who rose to world attention in August 1980 when he led a strike of shipyard workers here that ended with an agreement to set up independent trade unions, said he was both surprised and "very suspicious" when he first heard last Wednesday that he would be freed. Insisting that his release had been unconditional, he said: "I signed nothing; I put myself under no obligations; I joined nothing; I was simply released."

Aside from putting on weight, Walesa appeared to have changed little as a result of his 11 months in detention. In the 24 hours since his release, he has displayed the same canny political sense and feeling for symbolic gestures that marked him as a leader in August 1980.

In between talking with separate groups of foreign journalists, Walesa would appear at the window of his second-floor apartment to receive the cheers of crowds of well-wishers gathered outside. His replies to questions on sensitive matters such as Solidarity's future were vague, indicating that he was well aware of the risks and uncertainties he faces.

In one of his interviews this morning, Walesa said he felt like a "man let out on a tightrope below which is the exercise yard of a prison -- and the tightrope is greased." He added: "I don't intend to fall off."

Walesa's public statements will be carefully analyzed not only in Warsaw but also in Moscow and other Soviet Bloc capitals. In an interview with the British daily The Guardian, the Polish leader, Gen. Wojciech Jaruzelski, made it clear that the military authorities intend to keep a tight rein on Walesa.

"Walesa's future role in Polish affairs will depend on the discipline he displays and by his public utterances and declarations, especially to the Western press, as well as his future activity," Jaruzelski said.

The dilemma facing Walesa is that over-cautious public statements could lose him support among a population that has been radicalized by 11 months of martial law. Together with the general mood of happiness in Gdansk surrounding his release, it is already possible to detect unease at the fact that he is free but thousands of other Solidarity activists remain in custody.

Questioned about the Solidarity underground, which includes many of his former colleagues, Walesa said its leaders were "following the dictates of their consciences" and it was not for him to judge them. Promising to work for the release of those still detained, he said: "I am with those who are still inside and will be with them right to sharing the last slice of bread. I come from the same stock as they do."

Walesa said that, during his 11-month detention, he had spent much time thinking about peaceful methods for reaching "a real national agreement" in Poland. "I worked the methods out theoretically in my mind and now I must test them in practice," he said.

Asked about the mechanics of his release and the mystery surrounding his movements over the past few days, Walesa said he wrote a letter to Jaruzelski proposing a discussion on Monday, Nov. 8. The date, he said, was significant, indicating that the demonstrations and strikes set for Nov. 10 had been in his mind when he wrote that the two sides had had time to understand each other's strength.

Walesa was then visited at Arlamow where he was interned by the interior minister, Gen. Czeslaw Kiszczak, with whom he talked three to four hours "man to man." Walesa said that, after the conversation, he was convinced that the best he could expect was to be transferred to Bialoleka prison near Warsaw where several other Solidarity leaders are held.

Instead, he was phoned the next day by Kiszczak and told that he would be freed.

He was taken from Arlamow on Saturday to Otwock, near Warsaw, his first place of internment, and stayed there overnight. After the meeting at the prosecutor general's office, Walesa was driven back to Otwock for lunch and then on Sunday to Gdansk.

Saying, "I never go into ifs," Walesa refused to say where Poland's 16-month experiment in democracy went wrong. But he said he had been expecting the government to take a step like martial law and, at a meeting of Solidarity's National Commission on Dec. 11 and 12 last year, had "subconscious premonitions" of what was about to happen. Martial law was declared Dec. 13.

"Nobody notified me about it, but I was fully aware of what was going on. I acted as a responsible Pole who knew that this was a battle he could not win but could only multiply losses, unnecessary losses. I judged this to be a fact which, in the given moment was irreversible and indispensible and acted in such a way as not to multiply losses," Walesa said.

Walesa was arrested at his apartment at 3.30 a.m. on Dec. 13, part of a massive sweep of Solidarity activists throughout Poland.

Despite the government's crackdown on Dec. 13, Walesa said he believed that in the long run there could be "no return" from the Gdansk agreements that led to Solidarity's birth.

"The spirit of the Gdansk agreements was great and it is immortal. It cannot be defeated," he said.

Asked about the trade union bill under which Solidarity was dissolved last month and new trade unions set up, Walesa implicitly criticized a clause that allows only one union per factory until at least 1985. He said that union pluralism was a prerequisite for democracy and had been one of the central points of the Gdansk agreement.

In his interview with Western journalists, Walesa also clarified a mystery surrounding his reported refusal to meet with Deputy Premier Mieczyslaw Rakowski in the first days of martial law. Describing the incident as "a great misunderstanding," he said one of his guards had awakened him and announced that "Vice Premier Markowski" had come to see him.

Walesa replied that he didn't know any "Vice Premier Markowski," and refused to talk to him. He only learned later who his visitor had been when the guard said that Rakowski had been extremely angry at being turned away.

As Walesa was giving his interview, one of Solidarity's former underground leaders, Wladyslaw Frasyniuk, was put on trial in Wroclaw accused of organizing illegal strikes and demonstrations. Frasyniuk, a member of Solidarity's provisional coordinating commission, was arrested last month.Hella Pick of The Guardian also reported the following in her article about the interview with Gen. Jaruzelski :

Jaruzelski indicated that he is eager to end martial law. He defended the recently approved trade union bill as flexible enough for workers to form a genuine trade union movement.

Jaruzelski said he was aware his government had a credibility problem and that Poland's problems were far from a solution.

The military leader and premier provided written answers to questions submitted in advance, then answered other questions during an informal discussion.