Vienna — The release from detention of Poland's Solidarity chairman, Lech Walesa, is imminent, according to the Polish ambassador to Britain, Stefan Staniszewski.
The ambassador said Jan. 17 he did not know the exact date for the release, but added that ''the decision has been taken and it would be soon.'' He also said that martial law itself would be lifted within ''two or three weeks.''
Mr. Walesa is not under prison or camp internment like almost all his co-committee members. He is lodged in a government villa near Warsaw where he has been visited by his family and Roman Catholic Church officials.
If the Solidarity leader is released at an early date, it would obviously be a move of major importance. But the real implications would depend on the precise conditions under which Mr. Walesa was freed.
There appear to be several reasons why the authorities might be willing to release Mr. Walesa. One is Mr. Walesa's firm bargaining stance, which is supported by the Roman Catholic Church. Just as important is the increasingly serious state of the economy and the general situation of the country during a winter of exceptional severity. Some sign of conciliation might be deemed desirable by the government to increase support at home and better Poland's image abroad.
Poland's military rulers have made repeated efforts to persuade Walesa to enter negotiations and thus to repudiate the radicals in the union leadership. But Mr. Walesa has refused to resume his pre-martial law negotiations with the authorities until all the elected union leaders now in internment are free and able to take part.
The statements by Ambassador Staniszewski, an experienced diplomat, coincided with resumption by Warsaw Radio of the broadcast Sunday morning Catholic mass. This was a notable concession under the August 1980 strike settlements, which had been suspended since military rule was imposed five weeks ago.
The mass - and other concessions on radio programs - was one of a recent series of civil relaxations of martial law. Others were the resumption of public entertainment and the renewed publication of one of Poland's most widely read newspapers, the daily Zycie Warszawy - until Dec. 13 one of the government's liveliest press critics. This week some branches of the universities are also reopening.
Meanwhile, there was sign of government ''give'' on the perilous issue of price increases,which has so often rocked Polish governments since 1956. The government has now acknowledged that some planned hikes - up to 400 percent - are excessive, while planned pay rises are inadequate.
Commenting on Ambassador Staniszewski's statement concerning Walesa was US Sen. Larry Pressler, who had just returned from Warsaw. He was the first American legislator to visit Poland since martial law was ordered. While there he met for one hour with the Polish Primate Archbishop Jozef Glemp Jan. 16.
The senator, who sits on a congressional food aid committee, told reporters, ''It is good news if it is true that Walesa is being released, but the Senate would need to have some very clear signal about him and about the proper lifting martial law to make it change its mind about (restricting) aid.''
Before leaving Warsaw, Senator Pressler had revealed that the primate had asked for continuing US food aid despite the still unstable political situation in the country.
He had apparently told the primate that aid could not be resumed until Mr. Walesa was in fact freed and Solidarity leaders are able to take part in talks with the government.