WARSAW, Poland (AP) _ Solidarity founder Lech Walesa and the outlawed union movement's underground leaders are calling for a nationwide, 15-minute work stoppage on Feb. 28 to protest government plans to raise food prices.

The call came in a joint statement by Walesa and the Solidarity Temporary Coordinating Commission, known by its Polish initials TKK, circulated to Western correspondents in Warsaw on Wednesday.

It is believed to be the first time Walesa has joined a strike call since before martial law was imposed and Solidarity was suspended in December 1981.

Walesa said the work stoppage, to begin at noon, is not intended ''to weaken the economy.''

''Instead, we wish to manifest in a universal, simultaneous, effective and safe manner the views of public opinion on key issues,'' Walesa said in a statement issued from the southern town of Zakopane, where he is on vacation.

Walesa and the TKK charged that ''the authorities are preparing for huge price hikes ... They also deprive workers of their right to an 8-hour working day.''

New labor regulations that took effect this month allow state-run factories to extend the working day beyond eight hours.

''In order to cover up for organizational inefficiency at factories they suggest expanding working hours without any increase in workers' salaries,'' the TKK statement said.

The government has announced plans to raise food prices in March.

In a related development, state-run television reported that investigations were under way against Adam Michnik, a prominent dissident, and Bogdan Lis, a former underground leader, for taking part in ''a conspiratorial meeting of the so-called Temporary Coordinating Commission of Solidarity'' on Jan. 21.

The report cited two articles of the penal code banning participation in an illegal organization.The two men could receive up to three years in prison if convicted.

The TKK communique said Lis and Michnik attended the Jan. 21 meeting that approved the strike call.

Lis and Michnik were released from prison under a government amnesty last year.

Lis' release in December led the United States to lift its objections to Poland's application for membership in the International Monetary Fund, one of the U.S. sanctions imposed after the 1981 military crackdown.