President Carter's first weekend in the White House is expected to be punctuated by two demonstrations today within view of the Oval Office.

Thousands of right-to-life advocates are scheduled to converge on the city today by chartered bus, car and plane for the fourth annual protest against the 1973 Supreme Court decision that struck down state laws outlawing abortions in the first six months of pregnancy.

Also today, a smaller crowd of antiwar partisans is slated to gather on the Ellipse at noon to urge President Carter to stop production of the B-1 bomber.

The March of Life, as the antiabortion demonstration is called, has obtained a police department permit for 100,000 demonstrators to assemble on the west step of the Capitol at 1 p.m. today.

Following a rally, which will include speeches by sympathetic members of Congress, the demonstrators will march along the same route Thursday's inaugural parade took to the White House and then to the Ellipse for more speeches.

President Carter, who was actively opposed by right-to-life groups in last year's election because he would not support an antiabortion amendment to the Constitution, has declined an invitation to speak to the demonstrators.

"We had a telephoned 'no' from someone on his staff, but we have invited him again," said Nellie J. Gray, president of March for Life yesterday.

Gray said that a total of 16,000 red roses, which the March for Life people have chosen as a symbol of their movement, were delivered yesterday to members of Congress and to President Carter.

Demonstrators have been encouraged to visit their legislators during the morning hours today to urge a Constitutional amendment outlawing all abortions.

Most of the prolife demonstrators will arrive by chartered bus. Jack Hurley, coordinator for transportation, said parking space has been reserved for 1,500 out-of-town buses.

The Roman Catholic Church has been the backbone of the antiabortion movement. Church newspapers, which in many dioceses go to every Catholic family with a parish affiliation, have kept up a steady drumfire of antiabortion articles, editorials and encouragement to participate in today's protest. There will be rallies and vigils marking the day in many communities across the country in addition to the protest here.

The rally opposing the B-1 bomber is sponsored by a number of peace groups and coordinated by the American Friends Service Committee. Similar protests are slated in 121 cities across the country.